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Document and Entity Information - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Mar. 01, 2015	Dec. 31, 2014	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name		Esperion Therapeutics, Inc.
Entity Central Index Key		0001434868
Document Type		10-K
Document Period End Date		Dec. 31, 2014
Amendment Flag		false
Current Fiscal Year End Date		--12-31
Entity Well-known Seasoned Issuer		No
Entity Voluntary Filers		No
Entity Current Reporting Status		Yes
Entity Filer Category		Accelerated Filer
Entity Public Float			$ 244.4
Entity Common Stock, Shares Outstanding	20,425,860
Document Fiscal Year Focus		2014
Document Fiscal Period Focus		FY
Entity Listing, Par Value Per Share	$ 0.001

Condensed Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 85,038	$ 56,537
Short-term investments	20,803	3,525
Prepaid clinical development costs	366	196
Other prepaid and current assets	560	362
Total current assets	106,767	60,620
Property and equipment, net	780	81
Intangible assets	56	56
Long-term investments	35,741	17,537
Total assets	143,344	78,294
Current liabilities:
Accounts payable	2,040	2,232
Current portion of long-term debt	638
Accrued clinical development costs	1,978	884
Other accrued liabilities	835	1,087
Total current liabilities	5,491	4,203
Long-term debt, net of discount	4,299
Total liabilities	9,790	4,203
Commitments and contingencies (Note 5)
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized and no shares issued or outstanding as of December 31, 2014 and December 31, 2013
Common stock, $0.001 par value; 120,000,000 shares authorized as of December 31, 2014 and December 31,2013; 20,352,876 shares issued 20,343,325 outstanding at December 31, 2014 and 15,357,413 shares issued and 15,340,710 outstanding at December 31, 2013	20	15
Additional paid-in capital	238,031	142,142
Accumulated other comprehensive loss	(59)	(3)
Accumulated deficit	(104,438)	(68,063)
Total stockholders' equity	133,554	74,091
Total liabilities and stockholders' equity	$ 143,344	$ 78,294

Condensed Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2014	Dec. 31, 2013
Condensed Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	20,352,876	15,357,413
Common stock, shares outstanding	20,343,325	15,340,710

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating expenses:
Research and development	$ 25,302	$ 16,014	$ 7,998
General and administrative	10,922	6,745	2,206
Total operating expenses	36,224	22,759	10,204
Loss from operations	(36,224)	(22,759)	(10,204)
Interest expense.	(270)	(936)	(1,486)
Change in fair value of warrant liability		(2,587)	32
Other income (expense), net	119	194	(84)
Net loss	$ (36,375)	$ (26,088)	$ (11,742)
Net loss per common share (basic and diluted) (in dollars per share)	$ (2.22)	$ (3.31)	$ (36.31)
Weighted-average shares outstanding (basic and diluted)	16,374,102	7,885,921	323,382
Other comprehensive loss:
Unrealized loss on investments	$ (56)	$ (3)
Total comprehensive loss	$ (36,431)	$ (26,091)	$ (11,742)

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Common Stock.	Additional Paid-In Capital	Deficit Accumulated During the Development Stage	Accumulated Other Comprehensive Loss	Series A preferred stock	Series A-1 preferred stock	Total
Balance at Dec. 31, 2011					$ 23,975
Balance (in shares) at Dec. 31, 2011	307,742
Balance at Dec. 31, 2011		$ 201	$ (30,233)				$ (30,032)
Balance (in shares) at Dec. 31, 2011	307,742
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		41					41
Exercise of stock options (in shares)	38,736
Beneficial conversion feature from issuance of convertible notes		288					288
Stock-based compensation		80					80
Net loss			(11,742)				(11,742)
Balance at Dec. 31, 2012		610	(41,975)		23,975		(41,365)
Balance (in shares) at Dec. 31, 2012	346,478
Increase (Decrease) in Temporary Equity
Issuance of preferred stock in exchange for convertible promissory notes, net of issuance costs					$ 16,623	$ 7,750
Issuance of preferred stock in exchange for convertible promissory notes, net of issuance costs (in shares)					16,623,092	6,750,000
Issuance of Series A preferred stock, net of issuance costs					$ 16,880
Issuance of Series A preferred stock, net of issuance costs (in shares)					17,000,000
Preferred shares converted into common stock	$ 9	65,216			$ (57,478)	$ (7,750)	65,225
Preferred shares converted into common stock (in shares)	9,210,999				(57,598,092)	(6,750,000)
Balance (in shares) at Dec. 31, 2012	346,478
Increase (Decrease) in Stockholders' Equity
Early exercise of stock options and vesting of restricted stock		21					21
Early exercise of stock options and vesting of restricted stock (in shares)	25,765
Preferred shares converted into common stock	$ 9	65,216			$ (57,478)	$ (7,750)	65,225
Issuance of common stock from public offering, net of issuance costs	$ 6	72,188					72,194
Issuance of common stock from public offering, net of issuance costs (in shares)	5,750,000
Reclassification of warrants from liabilities to equity		2,852					2,852
Exercise of stock options		28					28
Exercise of stock options (in shares)	24,171
Stock-based compensation		1,227					1,227
Other comprehensive loss				$ (3)			(3)
Net loss			(26,088)				(26,088)
Balance at Dec. 31, 2013	$ 15	142,142	(68,063)	(3)			$ 74,091
Balance (in shares) at Dec. 31, 2013	15,357,413						15,357,413
Balance (in shares) at Dec. 31, 2013	15,357,413						15,357,413
Increase (Decrease) in Stockholders' Equity
Early exercise of stock options and vesting of restricted stock		39					$ 39
Issuance of common stock from public offering, net of issuance costs	$ 5	91,620					91,625
Issuance of common stock from public offering, net of issuance costs (in shares)	4,887,500
Issued warrants in connection with debt issuance		78					78
Exercise of stock options		473					$ 473
Exercise of stock options (in shares)	107,963						107,963
Stock-based compensation		3,679					$ 3,679
Other comprehensive loss				(56)			(56)
Net loss			(36,375)				(36,375)
Balance at Dec. 31, 2014	$ 20	$ 238,031	$ (104,438)	$ (59)			$ 133,554

Condensed Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net loss	$ (36,375)	$ (26,088)	$ (11,742)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	160	71	139
Amortization of debt discount and beneficial conversion	15	459	117
Amortization of debt issuance costs	16	19	15
Amortization of premiums and discounts on investments	202	47
Revaluation of warrants		2,587	(32)
Noncash interest expense on convertible notes		459	1,370
Stock-based compensation expense	3,679	1,227	80
Loss related to assets held for sale	29	27	87
Loss/(Gain) on sale of assets	2	(148)	(3)
Changes in assets and liabilities:
Prepaids and other assets	(332)	27	(429)
Accounts payable	(299)	1,756	(215)
Other accrued liabilities	882	1,443	(195)
Net cash used in operating activities	(32,021)	(18,114)	(10,808)
Investing activities
Purchases of investments	(48,088)	(24,677)
Proceeds from sales/maturities of investments	12,351	3,505
Proceeds from sale of assets	12	201	5
Purchase of property and equipment	(873)	(31)	(7)
Net cash used in investing activities	(36,598)	(21,002)	(2)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	91,731	72,194
Proceeds from issuance of preferred stock, net of issuance costs		16,824
Proceeds from exercise of common stock options	473	123	41
Proceeds from warrant issuance	78		298
Proceeds from debt issuance, net of issuance costs	4,838		15,412
Net cash provided by financing activities	97,120	89,141	15,751
Net increase in cash and cash equivalents	28,501	50,025	4,941
Cash and cash equivalents at beginning of period	56,537	6,512	1,571
Cash and cash equivalents at end of period	85,038	56,537	$ 6,512
Supplemental disclosure of cash flow information:
Deferred offering costs not yet paid	$ 107
10% Convertible promissory notes
Supplemental disclosure of cash flow information:
Conversion of promissory notes, including accrued interest into Series A - 1 preferred stock		16,623
Pfizer note
Supplemental disclosure of cash flow information:
Conversion of promissory notes, including accrued interest into Series A - 1 preferred stock		$ 7,803

The Company and Basis of Presentation

12 Months Ended

Dec. 31, 2014

The Company and Basis of Presentation

The Company and Basis of Presentation

1. The Company and Basis of Presentation

The Company is an emerging pharmaceutical company whose planned principal operations are focused on developing and commercializing first-in-class, oral, low-density lipoprotein cholesterol (“LDL-cholesterol”) lowering therapies for the treatment of hypercholesterolemia and other cardiometabolic risk markers. ETC-1002, the Company's lead product candidate, is a first-in-class, orally available, once-daily small molecule designed to lower LDL-cholesterol levels and avoid many of the side effects associated with other LDL-cholesterol lowering therapies currently available. ETC-1002 is being developed for patients with hypercholesterolemia. One completed Phase 2b clinical study and a second that is nearing completion build upon a successful and comprehensive Phase 1 and Phase 2 clinical development program for ETC-1002. The Company owns the exclusive worldwide rights to ETC-1002.

The Company's primary activities since incorporation have been conducting research and development activities, including nonclinical, preclinical and clinical testing, performing business and financial planning, recruiting personnel, and raising capital. Accordingly, the Company has not commenced principal operations and is subject to risks and uncertainties which include the need to research, develop, and clinically test potential therapeutic products; obtain regulatory approvals for its products and commercialize them, if approved; expand its management and scientific staff; and finance its operations with an ultimate goal of achieving profitable operations.

The Company has sustained operating losses since inception and expects such losses to continue over the foreseeable future. Management plans to continue to fund operations through public or private equity or debt financings or through other sources, which may include collaborations with third parties. If adequate funds are not available, the Company may not be able to continue the development of its current or future product candidates, or to commercialize its current or future product candidates, if approved.

Reverse Stock Split

On June 11, 2013, in connection with its initial public offering (the “IPO”), the Company effectuated a 1-for-6.986 reverse stock split of its outstanding common stock, which was approved by the Company's board of directors on June 5, 2013. The reverse stock split resulted in an adjustment to the Series A preferred stock and Series A-1 preferred stock conversion prices to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give effect to the reverse stock split for all periods presented. The shares of common stock retained a par value of $0.001 per share. Accordingly, the stockholders' equity reflects the reverse stock split by reclassifying from "common stock" to "Additional paid-in capital" in an amount equal to the par value of the decreased shares resulting from the reverse stock split.

Initial Public Offering

On July 1, 2013, the Company completed its IPO whereby the Company sold 5,000,000 shares of common stock at a price of $14.00 per share. The shares began trading on the Nasdaq Global Market on June 26, 2013. On July 11, 2013, the underwriters exercised their over-allotment option in full and purchased an additional 750,000 shares of common stock at a price of $14.00 per share. The Company received approximately $72.2 million in net proceeds from the IPO, including proceeds from the exercise of the underwriters' over-allotment option, net of underwriting discounts and commissions and offering expenses. Upon closing of the IPO, all outstanding shares of preferred stock converted into 9,210,999 shares of common stock; and warrants exercisable for convertible preferred stock were automatically converted into warrants exercisable for 277,690 shares of common stock, resulting in the reclassification of the related convertible preferred stock warrant liability of $2.9 million to additional paid-in capital (See Note 4).

The following table summarizes the Company's capitalization upon closing of its initial public offering:

Total common stock issued as of June 30, 2013			396,414
Conversion of Series A preferred stock into common stock upon closing of IPO			8,244,781
Conversion of Series A-1 preferred stock into common stock upon closing of IPO			966,218
Sales of common stock through IPO			5,000,000

Common stock issued as of July 1, 2013			14,607,413
Issuance of common stock to underwriters due to exercise of over-allotment			750,000

Total common stock issued as of July 11, 2013			15,357,413

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2014
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosures. Actual results could differ from those estimates. Prior to the completion of the IPO on July 1, 2013, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company's judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of its preferred stock, the superior rights and preferences of securities senior to its common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date. Cash and Cash Equivalents The Company invests its excess cash in bank deposits, money market accounts, and short-term investments. The Company considers all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are reported at fair value. Investments Investments are considered to be available-for-sale and are carried at fair value. Unrealized gains and losses, if any, are reported as a separate component of stockholders' equity. The cost of investments classified as available-for-sale are adjusted for the amortization of premiums and accretion of discounts to maturity and recorded in other income (expense), net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income (expense), net. Investments with original maturities beyond 90 days at the date of purchase and which mature at, or less than twelve months from, the balance sheet date are classified as current. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term. Concentration of Credit Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to concentrations of credit risk. The Company has established guidelines for investment of its excess cash and believes the guidelines maintain safety and liquidity through diversification of counterparties and maturities. Segment Information The Company views its operations and manages its business in one operating segment, which is the business of researching, developing and commercializing therapies for the treatment of patients with elevated levels of LDL-cholesterol and other cardiometabolic risk markers. Fair Value of Financial Instruments The Company's cash, cash equivalents and investments are carried at fair value. Financial instruments, including other prepaid and current assets, accounts payable and accrued liabilities are carried at cost, which approximates fair value. Debt is carried at amortized cost, which approximates fair value. Property and Equipment, Net Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets, generally three to ten years. Leasehold improvements are amortized over the lesser of the lease term or the estimated useful lives of the related assets. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment loss, if recognized, would be based on the excess of the carrying value of the impaired asset over its respective fair value. Excluding impairment losses recorded on assets held for sale, no other impairment losses have been recorded through December 31, 2014. Research and Development Research and development expenses consist of costs incurred to further the Company's research and development activities and include salaries and related benefits, costs associated with study studies, nonclinical activities (such as toxicology studies), regulatory activities, manufacturing activities to support clinical activities, research-related overhead expenses, and fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company. Research and development costs are expensed as incurred. In-Process Research and Development In April 2008, the Company acquired certain tangible research and development assets and intellectual property from Pfizer Inc. (“Pfizer”). As the acquired in-process research and development had not reached technological feasibility and had no alternative future uses in connection with this asset and intellectual property acquisition and the related purchase price allocation, the Company expensed $0.1 million as in-process research and development costs in 2008. Accrued Clinical Development Costs Outside research costs are a component of research and development expense. These expenses include fees paid to contract research organizations and other service providers that conduct certain clinical and product development activities on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management's estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly. Income Taxes The Company utilizes the liability method of accounting for income taxes as required by ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and the tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has incurred operating losses since inception. Accordingly, it is not more likely than not that the Company will realize deferred tax assets and as such, it has recorded a full valuation allowance. Warrants The Company accounts for its warrants issued in connection with its various financing transactions based upon the characteristics and provisions of the instrument. Warrants classified as liabilities are recorded on the Company's balance sheet at their fair value on the date of issuance and are marked-to-market on each subsequent reporting period, with the fair value changes recognized in the statement of operations. Warrants classified as additional-paid-in-capital are recorded on the Company's balance sheet at their fair value on the date of issuance. The warrants are measured using the Black-Scholes option-pricing model subsequent to the pricing of the Company's IPO and a Monte Carlo valuation model for previous periods which are based, in part, upon inputs where there is little or no market data, requiring the Company to develop its own independent assumptions. (See Note 4). Stock-Based Compensation The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation—Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value calculated using a Black-Scholes option pricing model. Additionally, under the provisions of ASC 718, the Company is required to include an estimate of the number of awards that will be forfeited in calculating compensation costs. Any changes to the estimated forfeiture rates are accounted for prospectively. Stock-based compensation arrangements with non-employees are recognized at the grant-date fair value and then re-measured at each reporting period. Expense is recognized during the period the related services are rendered. Recent Accounting Pronouncements In June 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-10 which improves financial reporting by reducing the cost and complexity associated with the incremental reporting requirements for development stage entities without reducing the relevance of information provided to users of financial statements. Under the amended guidance, issuers are no longer required to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage. The Company adopted the amendment which resulted in a reduction in disclosures previously relating to a development stage entity. In August 2014, the FASB issued ASU 2014-15 which requires management of public companies to evaluate whether there are conditions and events that raise substantial doubt about the entity's ability to continue as a going concern within one year after the financial statements are issued and, if so, to disclose that fact. Management will be required to make this evaluation for both annual and interim reporting periods, if applicable. Management is also required to evaluate and disclose whether its plans alleviate that doubt. The standard is effective for annual periods ending after December 15, 2016 and interim periods within annual periods beginning after December 15, 2016. Early adoption is permitted for annual or interim reporting periods for which the financial statements have not previously been issued. The Company does not believe the adoption of this standard will have a material impact on its financial position, results of operations or related financial statement disclosures.

Debt

12 Months Ended

Dec. 31, 2014

Debt

Debt

3. Debt

Credit Facility

In June 2014, the Company entered into a loan and security agreement (the "Credit Facility") with Oxford Finance LLC which provides for initial borrowings of $5.0 million under term loans ("Term A Loan") and additional borrowings of $15.0 million ("Term B Loan") at the Company's option, for a maximum of $20.0 million. On June 30, 2014, the Company received proceeds of $5.0 million from the issuance of secured promissory notes under the Term A Loan. The remaining $15.0 million available under Term B Loan becomes available to be drawn down, at the Company's sole discretion, until March 31, 2015, upon achieving positive development results in the Company's ongoing Phase 2b clinical study (a "Milestone Event"). All secured promissory notes issued under the Credit Facility are due on July 1, 2018 and are collateralized by substantially all of the Company's personal property, other than its intellectual property.

The Company is obligated to make monthly, interest-only payments on Term A Loan until July 1, 2015 and, thereafter, to pay 36 consecutive equal monthly installments of principal and interest from August 1, 2015 through July 1, 2018. If a Milestone Event is achieved and the Company elects to make additional borrowings under the Term B Loan, the term of monthly, interest-only payments will be extended until January 1, 2016. Term A Loan bears interest at an annual rate of 6.40%. In the event the Company enters into Term B Loan, the interest rate will be the greater of (i) 6.40% or (ii) three month LIBOR rate three business days prior to the funding of the new term loan plus an additional 6.17%. In addition, a final payment equal to 8.0% of any amounts drawn under the Credit Facility is due upon the earlier of the maturity date or prepayment of the term loans. The Company is recognizing the final payment as interest expense using the effective interest method over the life of the Credit Facility.

There are no financial covenants associated to the Credit Facility. However, so long as the Credit Facility is outstanding, there are negative covenants that limit or restrict the Company's activities, which include limitations on incurring indebtedness, granting liens, mergers or acquisitions, dispositions of assets, making certain investments, entering into certain transactions with affiliates, paying dividends or distributions, encumbering or pledging interest in its intellectual property and certain other business transactions. Additionally, the Credit Facility also includes events of default, the occurrence and continuation of any of which provides the lenders the right to exercise remedies against the Company and the collateral securing the loans under the Credit Facility, which includes cash. These events of default include, among other things, non-payment of any amounts due under the Credit Facility, insolvency, the occurrence of a material adverse event, inaccuracy of representations and warranties, cross default to material indebtedness and a material judgment against the Company. Upon the occurrence of an event of default, all obligations under the Credit Facility shall accrue interest at a rate equal to the fixed annual rate plus five percentage points.

In connection with the borrowing of Term A Loan, the Company issued a warrant (the "Warrant") to purchase 8,230 shares of common stock at an exercise price of $15.19 (see Note 4). The Warrant resulted in a debt discount of $0.1 million which is amortized into interest expense using the effective interest method over the life of Term A Loan. In addition, deferred financing costs of $0.1 million included in other prepaid and current assets on the consolidated balance sheet as of December 31, 2014 are amortized to interest expense using the effective-interest method over the same term. As of December 31, 2014, the remaining unamortized discount and debt issuance costs associated with the debt were $0.1 million and $0.1 million, respectively.

Estimated future principal payments due under the Credit Facility are as follows:

Years Ending December 31,	(in thousands)
2014	$	—
2015		638
2016		1,604
2017		1,709
2018		1,049

Total	$	5,000

During the year ended December 31, 2014, the Company recognized $0.3 million of interest expense and made cash interest payments of $0.1 million related to the Credit Facility.

Convertible Notes

In January 2012, the Company issued $6.0 million of 10% convertible promissory notes to certain existing investors for cash. In September and November 2012, the Company issued the aggregate of $9.7 million of 10% convertible promissory notes that mature on September 4, 2013 for cash to certain existing investors. In connection with the September convertible note financing, the Company and the holders of the January 2012 convertible promissory notes agreed to extend the maturity date of the January 2012 notes to September 4, 2013. In February 2013, these convertible promissory notes, with an outstanding principal of $15.7 million and accrued interest of $0.9 million, were amended and then converted into 16,623,092 shares of Series A preferred stock, in accordance with their terms and at their conversion price of $1.00 per share, and following such conversion, the notes were cancelled.

The holders of the September convertible promissory notes received the benefit of a deemed conversion price of the September convertible promissory notes that were below the estimated fair value of the Series A convertible preferred stock at the time of their issuance. The fair value of this beneficial conversion feature was estimated to be $0.3 million. The fair value of this beneficial conversion feature was recorded to debt discount and amortized to interest expense using the effective interest method over the term of the convertible promissory notes. As a result of the conversion of the convertible promissory notes into shares of Series A preferred stock in February 2013, the Company recorded the remaining accretion of the beneficial conversion feature of $0.2 million as interest expense during the year ended December 31, 2013.

In connection with the issuance of the September and the November 2012 convertible promissory notes, the Company issued warrants to purchase shares of Series A preferred stock for an aggregate price of $9,700. The estimated fair value of the warrants at issuance was $0.3 million. The proceeds from the sale of the preferred stock and warrants were allocated with $9.4 million to the convertible promissory notes and $0.3 million to warrants. This resulted in a discount on the convertible promissory notes which was amortized into interest expense, using the effective interest method, over the life of the convertible promissory notes (see Note 4). The company recorded $0.1 million of interest expense for the accretion of the discount during the year ended December 31, 2012. As a result of the conversion of the convertible promissory notes into shares of Series A preferred stock in February 2013, the Company recorded $0.2 million of interest expense for the accretion of this discount during the year ended December 31 2013.

In April 2008, the Company acquired all of the capital stock of Esperion from Pfizer in exchange for a non-subordinated convertible note in the original principal amount of $5.0 million. This convertible promissory note had a maturity date of April 28, 2018. The note bore interest at 8.931% annually, payable semiannually on June 30 and December 31 by adding such unpaid interest to the principal of the note, which would thereafter accrue interest. The Company accrued interest of $0.3 million and $0.6 million during the years ended December 31, 2013 and 2012, respectively. In May 2013 the Company entered into a stock purchase agreement with Pfizer Inc. and sold 6,750,000 shares of Series A-1 preferred stock at a price of $1.1560 per share, which was the fair value at the transaction date. The purchase price was paid through the cancellation of all outstanding indebtedness, including accrued interest, under the Pfizer convertible promissory note, which had an outstanding balance, including accrued interest, of $7.8 million as of May 29, 2013. The Series A-1 preferred stock issued in connection with this transaction was subsequently converted into 966,218 shares of common stock upon completion of the IPO on July 1, 2013.

Commitments and contingencies

12 Months Ended

Dec. 31, 2014

Commitments and contingencies

Commitments and contingencies

5. Commitments and contingencies

In February 2014, the Company entered into an operating lease agreement for its principal executive offices located in Ann Arbor, Michigan commencing in April 2014 with a term of 63 months. The Company's lease provides for fixed monthly rent for the term of the lease, with monthly rent increasing every 12 months subsequent to the first three months of the lease, and also provides for certain rent adjustments to be paid as determined by the landlord.

In May 2014, the Company entered into the third amendment to the operating lease agreement for its laboratory facility in Plymouth, Michigan. The amendment provides in part that (i) the expiration date of the term of the lease is extended from April 2014 to April 2017, (ii) the rentable laboratory space is adjusted to 3,045 square feet, (iii) the Company's proportionate share of the landlord's expenses and taxes is adjusted to 7.40%, (iv) the Company may exercise its option to renew the lease for one term of three years through written notice to the landlord by February 2017 and (v) the annual base rent under the lease is decreased to $37,000, subject to increase and adjustments provided in the lease.

The total rent expense for the years ended December 31, 2014, 2013 and 2012 was approximately $0.3 million, $0.3 million and $0.3 million, respectively. The following table summarizes the Company's future minimum lease payments as of December 31, 2014:

	Total		Less than 1 Year		1 - 3 Years		3 - 5 Years		More than 5 Years
	(in thousands)
Operating lease	$	552	$	133	$	251	$	168	$	—

Total	$	552	$	133	$	251	$	168	$	—

The Company also holds a license agreement in which it is obligated to make future minimum annual payments of $50,000 in years where there is not a milestone payment required under the terms of the agreement (see Note 14). Further, the Company is contractually obligated to issue up to an aggregate of 11,451 shares of common stock upon meeting various future milestones set forth in the agreement.

Property and Equipment

12 Months Ended

Dec. 31, 2014

Property and Equipment

Property and Equipment

6. Property and Equipment

Property and equipment consist of the following:

	December 31,
	2014		2013
	(in thousands)
Lab equipment	$	519	$	511
Computer equipment		110		100
Software		74		119
Furniture and fixtures		320		11
Leasehold improvements		158		21
Assets in Progress		2		7

Subtotal		1,183		769
Less accumulated depreciation and amortization		403		688

Property and equipment, net	$	780	$	81

Depreciation expense was $0.2 million, $0.1 million, and $0.1 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Investments

12 Months Ended

Dec. 31, 2014

Investments

Investments

8. Investments

The following table summarizes the Company's cash equivalents and investments:

	December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash equivalents:
Money market funds	$	357	$	—	$	—		$	357

Short-term investments:
Certificates of deposit		2,934		—		—			2,934
U.S treasury notes		9,020		4		—			9,024
U.S. government agency securities		8,853		—		(8	)		8,845
Long-term investments:
Certificates of deposit		1,848		—		—			1,848
U.S. treasury notes		2,494		—		(5	)		2,489
U.S. government agency securities		31,454		—		(50	)		31,404

Total	$	56,960	$	4	$	(63	)	$	56,901


	December 31, 2013
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash equivalents:
Money market funds	$	5,356	$	—	$	—		$	5,356

Short-term investments:
U.S treasury notes		2,071		—		—			2,071
U.S. government agency securities		1,454		—		—			1,454
Long-term investments:
Certificates of deposit		238		—		—			238
U.S. treasury notes		9,116		3		(2	)		9,117
U.S. government agency securities		8,187		1		(5	)		8,183

Total	$	26,422	$	4	$	(7	)	$	26,419

At December 31, 2014, remaining contractual maturities of available-for-sale investments classified as current on the balance sheet were less than 12 months, and remaining contractual maturities of available-for-sale investments classified as long-term were less than two years.

There were no unrealized gains or losses on investments reclassified from accumulated other comprehensive income to other income (expense) in the Statement of Operations during the year ended December 31, 2014.

Fair Value Measurements

12 Months Ended

Dec. 31, 2014

Fair Value Measurements

Fair Value Measurements

9. Fair Value Measurements

The Company follows accounting guidance that emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Fair value is defined as "the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date." Fair value measurements are defined on a three level hierarchy:

Level 1 inputs:		Quoted prices for identical assets or liabilities in active markets;
Level 2 inputs:		Observable inputs other than Level 1 prices, such as quoted market prices for similar assets or liabilities or other inputs that are observable or can be corroborated by market data; and
Level 3 inputs:		Unobservable inputs that are supported by little or no market activity and require the reporting entity to develop assumptions that market participants would use when pricing the asset or liability.

The following table presents the Company's financial assets and liabilities that have been measured at fair value on a recurring basis:


Description	Total		Level 1		Level 2		Level 3
	(in thousands)
December 31, 2014
Assets:
Money market funds	$	357	$	357	$	—	$	—
Available-for-sale securities:
Certificates of deposit		4,782		4,782		—		—
U.S. treasury notes		11,513		11,513		—		—
U.S. government agency securities		40,249		—		40,249		—

Total assets at fair value	$	56,901	$	16,652	$	40,249	$	—


December 31, 2013
Assets:
Money market funds	$	5,356	$	5,356	$	—	$	—
Available-for-sale securities:
Certificates of deposit		238		238		—		—
U.S. treasury notes		11,188		11,188		—		—
U.S. government agency securities		9,637		—		9,637		—

Total assets at fair value	$	26,419	$	16,782	$	9,637	$	—

There were no transfers between Levels 1, 2 or 3 during the year ended December 31, 2014 or December 31, 2013.

Fair Value Measurements on a Nonrecurring Basis

In addition to items that are measured at fair value on a recurring basis, the Company also measures assets held for sale at the lower of its carrying amount or fair value on a nonrecurring basis. The Company recognized an impairment expense and other losses relating to assets held for sale during the year ended December 31, 2014, 2013, and 2012 of $0, less than $0.1 million, and $0.1 million based on recent market sales data for similar equipment less the related costs to sell and recent purchase offers, which are Level 3 inputs. There are no assets held for sale as of December 31, 2014.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Stock Compensation

12 Months Ended

Dec. 31, 2014

Stock Compensation

Stock Compensation

11. Stock Compensation

2013 Stock Option and Incentive Plan

On June 7, 2013, the Company's stockholders approved the 2013 Stock Option and Incentive Plan (the "2013 Plan"), which became effective on June 25, 2013. The number of shares of stock reserved and available for issuance under the 2013 Plan is the sum of (i) 1,100,000, plus (ii) 54,129 shares originally reserved under the Company's 2008 Incentive Stock Option and Restricted Stock Plan (the "2008 Plan") that became available for issuance under the 2013 Plan upon completion of the Company's initial public offering, plus (iii) the shares underlying any awards granted under the 2008 Plan that are forfeited, canceled, held back upon the exercise of an option or settlement of an award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock or otherwise terminated (other than by exercise). Additionally, on each January 1 the number of shares reserved and available for issuance under the 2013 Plan shall be cumulatively increased by two and a half percent of the number of shares issued and outstanding on the immediately preceding December 31 or such lesser number of shares as determined by the plan administrator.

2008 Stock Option and Restricted Stock Plan

In April 2008, the Company adopted the 2008 Plan, administered by the Board of Directors or a committee appointed by the Board of Directors. The 2008 Plan provides for the granting of stock options and restricted stock to employees and nonemployees of the Company. Options granted under the 2008 Plan may either be incentive stock options (“ISO”s), restricted stock awards (“RSA”s) or nonqualified stock options (“NQSO”s). Stock options and restricted stock grants may be granted to employees, directors and consultants.

Stock awards under the 2008 Plan may be granted for up to ten years from the adoption of the 2008 Plan at prices no less than 100 percent of the fair value of the shares on the date of the grant as determined by (i) the closing price of the Company's common stock on any national exchange, (ii) the National Association of Securities Dealers Inc. Automated Quotation System (“NASDAQ”), if so authorized for quotation as a NASDAQ security, or (iii) by reasonable application of a reasonable valuation method. The valuation methods utilized by the Company are consistent with the AICPA Technical Practice Aid.

Under the 2013 Plan and the 2008 Plan the vesting of options granted or restricted awards given will be determined individually with each option grant. Generally, 25 percent of the granted amount will vest upon the first anniversary of the option grant with the remainder vesting ratably on the first day of each calendar quarter for the following three years. Stock options have a 10 year life and expire if not exercised within that period, or if not exercised within 90 days of cessation of providing service to the Company.

The following table summarizes the activity relating to the Company's options to purchase common stock for the year ended December 31, 2014:

	Number of Options			Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at December 31, 2013		1,401,101		$	9.59		8.95	$	7,755
Granted		561,500		$	15.03
Forfeited or expired (vested and unvested)		(125,052	)	$	12.97
Exercised		(107,963	)	$	4.38

Outstanding at December 31, 2014		1,729,586		$	11.44		8.43	$	50,155

The following table summarizes information about the Company's stock option plan as of December 31, 2014:

	Number of Options		Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
							(in thousands)
Vested and expected to vest at December 31, 2014		1,671,313	$	11.37		8.41	$	48,588

Exercisable at December 31, 2014		752,397	$	6.61		7.58	$	25,452

The total intrinsic value of stock options exercised during the years ended December 31, 2014, 2013 and 2012 was $1.4 million, $0.2 million and less than $0.1 million, respectively.

The following table shows the weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees and non-employees during the period from December 31, 2012 to December 31, 2014, using the Black-Scholes option pricing model:

	Year ended December 31,
	2014			2013			2012
Risk-free interest rate		1.81	%		1.45	%		0.85	%
Dividend yield		—			—			—
Weighted-average expected life of options (years)		6.32			6.26			6.25
Volatility		75	%		74	%		80	%

The risk-free interest rate assumption was based on the United States Treasury's rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued. The assumed dividend yield was based on the Company's expectation of not paying dividends in the foreseeable future. The weighted-average expected life of the options was calculated using the simplified method as prescribed by the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin No. 107 (“SAB No. 107”). This decision was based on the lack of relevant historical data due to the Company's limited historical experience. In addition, due to the Company's limited historical data, the estimated volatility also reflects the application of SAB No. 107, incorporating the historical volatility of comparable companies whose share prices are publicly available.

The weighted-average grant-date fair values of stock options granted during the years ended December 31, 2014, 2013, and 2012 were $10.15, $7.14, and $1.33 respectively. During the years ended December 31, 2014, 2013, and 2012, the Company recognized stock-based compensation expense of $3.7 million, $1.2 million, and $0.1 million, respectively.

As of December 31, 2014, there was approximately $9.3 million of unrecognized compensation cost related to unvested options, adjusted for forfeitures, which will be recognized over a weighted-average period of approximately 2.9 years.

Income Taxes

12 Months Ended

Dec. 31, 2014

Income Taxes

Income Taxes

13. Income Taxes

There was no provision for income taxes for the years ended December 31, 2014, 2013 and 2012 because the Company has incurred operating losses since inception. At December 31, 2014, the Company has concluded that it is not more likely than not that the Company will realize the benefit of its deferred tax assets due to its history of losses. Accordingly, the net deferred tax assets have been fully reserved.

As of December 31, 2014, 2013 and 2012, the Company had deferred tax assets, before valuation allowance, of approximately $34.2 million, $22.8 million and $14.4 million, respectively. Realization of the deferred assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance.

As of December 31, 2014, 2013 and 2012, the Company had federal net operating loss carryforwards of approximately $95.1 million, $62.3 million and $40.5 million, respectively. The federal net operating loss will expire at various dates beginning in 2028, if not utilized. As of December 31, 2014, 2013 and 2012, the Company had state net operating loss carryforwards of approximately $16.6 million, $33.1 million and $11.3 million, respectively. The state net operating loss will expire at various dates beginning in 2022, if not utilized. The Company has $0.5 million of NOLs related to excess tax benefits generated upon the settlement of stock awards that increased a current year net operating loss. The Company cannot record the benefit of these losses in the financial statements until the losses are utilized to reduce its income taxes payable at which time it will recognize the tax benefit in equity.

A reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate is as follows:

	December 31,
	2014			2013			2012
Federal income tax (benefit) at statutory rate		(34.0	)%		(34.0	)%		(34.0	)%
Change in Tax Rate		2.1	%		—	%		—	%
Permanent items		1.0	%		4.9	%		0.4	%
Other		0.1	%		—	%		(0.2	)%
Change in valuation allowance		30.8	%		29.1	%		33.8	%

Effective income tax rate		0.0	%		0.0	%		0.0	%

If the Company experiences a greater than 50 percentage point aggregate change in ownership of certain significant stockholders over a three-year period, a Section 382 ownership change could be deemed to have occurred. If a section 382 change occurs, the Company's future utilization of the net operating loss carryforwards and credits as of the ownership change will be subject to an annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended, and similar state provisions. Such an annual limitation may result in the expiration of net operating losses before utilization.

The Company's reserves related to taxes are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. The Company recognized no material adjustment for unrecognized income tax benefits. Through December 31, 2014, the Company had no unrecognized tax benefits or related interest and penalties accrued.

Significant components of the Company's deferred tax assets are summarized in the table below:

	December 31,
	2014			2013
	(in thousands)
Deferred tax assets:
Federal and state operating loss carryforwards	$	33,099		$	22,485
Equity Compensation		971			206
Temporary differences		138			113

Total deferred tax assets		34,208			22,804
Valuation allowance		(34,208	)		(22,804	)

Net deferred tax assets	$	—		$	—

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2014

Selected Quarterly Financial Data (Unaudited)

Selected Quarterly Financial Data (Unaudited)

16. Selected Quarterly Financial Data (Unaudited)

The following table summarizes the unaudited quarterly financial data for the last two years:

	2014
	March 31			June 30			September 30			December 31
	(in thousands, except share and per share data)
Operating expenses:
Research and development	$	5,400		$	6,528		$	7,174		$	6,200
General and administrative		2,490			2,726			2,526			3,180

Total operating expenses		7,890			9,254			9,700			9,380
Loss from operations:		(7,890	)		(9,254	)		(9,700	)		(9,380	)

Interest expense		—			(1	)		(135	)		(134	)
Change in fair value of warrant liability		—			—			—			—
Other income (expense), net		16			17			29			57

Net loss	$	(7,874	)	$	(9,238	)	$	(9,806	)	$	(9,457	)


Net loss per common share (basic and diluted)	$	(0.51	)	$	(0.60	)	$	(0.64	)	$	(0.49	)
Weighted-average shares outstanding (basic and diluted)		15,369,055			15,399,018			15,432,641			19,276,639

	2013
	March 31			June 30			September 30			December 31
Operating expenses:
Research and development	$	2,093		$	3,100		$	3,483		$	7,338
General and administrative		1,251			1,172			1,924			2,398

Total operating expenses		3,344			4,272			5,407			9,736
Loss from operations:		(3,344	)		(4,272	)		(5,407	)		(9,736	)

Interest expense		(828	)		(108	)		—			—
Change in fair value of warrant liability		(42	)		(2,545	)		—			—
Other income (expense), net		(25	)		4			169			46

Net loss	$	(4,239	)	$	(6,921	)	$	(5,238	)	$	(9,690	)


Net loss per common share (basic and diluted)	$	(12.24	)	$	(19.82	)	$	(0.34	)	$	(0.63	)
Weighted-average shares outstanding (basic and diluted)		346,478			349,170			15,253,704			15,340,713

The Company and Basis of Presentation (Policies)	12 Months Ended
The Company and Basis of Presentation (Policies)	Dec. 31, 2014
The Company and Basis of Presentation
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosures. Actual results could differ from those estimates. Prior to the completion of the IPO on July 1, 2013, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company's judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of its preferred stock, the superior rights and preferences of securities senior to its common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company invests its excess cash in bank deposits, money market accounts, and short-term investments. The Company considers all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are reported at fair value.
Investments	Investments Investments are considered to be available-for-sale and are carried at fair value. Unrealized gains and losses, if any, are reported as a separate component of stockholders' equity. The cost of investments classified as available-for-sale are adjusted for the amortization of premiums and accretion of discounts to maturity and recorded in other income (expense), net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income (expense), net. Investments with original maturities beyond 90 days at the date of purchase and which mature at, or less than twelve months from, the balance sheet date are classified as current. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term.
Concentration of Credit Risk	Concentration of Credit Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to concentrations of credit risk. The Company has established guidelines for investment of its excess cash and believes the guidelines maintain safety and liquidity through diversification of counterparties and maturities.
Segment Information	Segment Information The Company views its operations and manages its business in one operating segment, which is the business of researching, developing and commercializing therapies for the treatment of patients with elevated levels of LDL-cholesterol and other cardiometabolic risk markers.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company's cash, cash equivalents and investments are carried at fair value. Financial instruments, including other prepaid and current assets, accounts payable and accrued liabilities are carried at cost, which approximates fair value. Debt is carried at amortized cost, which approximates fair value.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets, generally three to ten years. Leasehold improvements are amortized over the lesser of the lease term or the estimated useful lives of the related assets.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment loss, if recognized, would be based on the excess of the carrying value of the impaired asset over its respective fair value. Excluding impairment losses recorded on assets held for sale, no other impairment losses have been recorded through December 31, 2014.
Research and Development	Research and Development Research and development expenses consist of costs incurred to further the Company's research and development activities and include salaries and related benefits, costs associated with study studies, nonclinical activities (such as toxicology studies), regulatory activities, manufacturing activities to support clinical activities, research-related overhead expenses, and fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company. Research and development costs are expensed as incurred.
In-Process Research and Development	In-Process Research and Development In April 2008, the Company acquired certain tangible research and development assets and intellectual property from Pfizer Inc. (“Pfizer”). As the acquired in-process research and development had not reached technological feasibility and had no alternative future uses in connection with this asset and intellectual property acquisition and the related purchase price allocation, the Company expensed $0.1 million as in-process research and development costs in 2008.
Accrued Clinical Development Costs	Accrued Clinical Development Costs Outside research costs are a component of research and development expense. These expenses include fees paid to contract research organizations and other service providers that conduct certain clinical and product development activities on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management's estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.
Income Taxes	Income Taxes The Company utilizes the liability method of accounting for income taxes as required by ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and the tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has incurred operating losses since inception. Accordingly, it is not more likely than not that the Company will realize deferred tax assets and as such, it has recorded a full valuation allowance.
Warrants	Warrants The Company accounts for its warrants issued in connection with its various financing transactions based upon the characteristics and provisions of the instrument. Warrants classified as liabilities are recorded on the Company's balance sheet at their fair value on the date of issuance and are marked-to-market on each subsequent reporting period, with the fair value changes recognized in the statement of operations. Warrants classified as additional-paid-in-capital are recorded on the Company's balance sheet at their fair value on the date of issuance. The warrants are measured using the Black-Scholes option-pricing model subsequent to the pricing of the Company's IPO and a Monte Carlo valuation model for previous periods which are based, in part, upon inputs where there is little or no market data, requiring the Company to develop its own independent assumptions. (See Note 4).
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation—Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value calculated using a Black-Scholes option pricing model. Additionally, under the provisions of ASC 718, the Company is required to include an estimate of the number of awards that will be forfeited in calculating compensation costs. Any changes to the estimated forfeiture rates are accounted for prospectively. Stock-based compensation arrangements with non-employees are recognized at the grant-date fair value and then re-measured at each reporting period. Expense is recognized during the period the related services are rendered.

Investments (Tables)

12 Months Ended

Dec. 31, 2014

Investments

Summary of the Company's cash equivalents and investments

	December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash equivalents:
Money market funds	$	357	$	—	$	—		$	357

Short-term investments:
Certificates of deposit		2,934		—		—			2,934
U.S treasury notes		9,020		4		—			9,024
U.S. government agency securities		8,853		—		(8	)		8,845
Long-term investments:
Certificates of deposit		1,848		—		—			1,848
U.S. treasury notes		2,494		—		(5	)		2,489
U.S. government agency securities		31,454		—		(50	)		31,404

Total	$	56,960	$	4	$	(63	)	$	56,901

	December 31, 2013
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash equivalents:
Money market funds	$	5,356	$	—	$	—		$	5,356

Short-term investments:
U.S treasury notes		2,071		—		—			2,071
U.S. government agency securities		1,454		—		—			1,454
Long-term investments:
Certificates of deposit		238		—		—			238
U.S. treasury notes		9,116		3		(2	)		9,117
U.S. government agency securities		8,187		1		(5	)		8,183

Total	$	26,422	$	4	$	(7	)	$	26,419

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value Measurements

Schedule of the Company's financial assets and liabilities that have been measured at fair value on a recurring basis

Description	Total		Level 1		Level 2		Level 3
	(in thousands)
December 31, 2014
Assets:
Money market funds	$	357	$	357	$	—	$	—
Available-for-sale securities:
Certificates of deposit		4,782		4,782		—		—
U.S. treasury notes		11,513		11,513		—		—
U.S. government agency securities		40,249		—		40,249		—

Total assets at fair value	$	56,901	$	16,652	$	40,249	$	—


December 31, 2013
Assets:
Money market funds	$	5,356	$	5,356	$	—	$	—
Available-for-sale securities:
Certificates of deposit		238		238		—		—
U.S. treasury notes		11,188		11,188		—		—
U.S. government agency securities		9,637		—		9,637		—

Total assets at fair value	$	26,419	$	16,782	$	9,637	$	—

Stock Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Stock Compensation

Summary of activity relating to the Company's options to purchase common stock

	Number of Options			Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at December 31, 2013		1,401,101		$	9.59		8.95	$	7,755
Granted		561,500		$	15.03
Forfeited or expired (vested and unvested)		(125,052	)	$	12.97
Exercised		(107,963	)	$	4.38

Outstanding at December 31, 2014		1,729,586		$	11.44		8.43	$	50,155

Summary of information about the stock option plan

	Number of Options		Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
							(in thousands)
Vested and expected to vest at December 31, 2014		1,671,313	$	11.37		8.41	$	48,588

Exercisable at December 31, 2014		752,397	$	6.61		7.58	$	25,452

Schedule of weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees and non-employees

	Year ended December 31,
	2014			2013			2012
Risk-free interest rate		1.81	%		1.45	%		0.85	%
Dividend yield		—			—			—
Weighted-average expected life of options (years)		6.32			6.26			6.25
Volatility		75	%		74	%		80	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2014

Income Taxes

Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate

	December 31,
	2014			2013			2012
Federal income tax (benefit) at statutory rate		(34.0	)%		(34.0	)%		(34.0	)%
Change in Tax Rate		2.1	%		—	%		—	%
Permanent items		1.0	%		4.9	%		0.4	%
Other		0.1	%		—	%		(0.2	)%
Change in valuation allowance		30.8	%		29.1	%		33.8	%

Effective income tax rate		0.0	%		0.0	%		0.0	%

Schedule of significant components of the Company's deferred tax assets

	December 31,
	2014			2013
	(in thousands)
Deferred tax assets:
Federal and state operating loss carryforwards	$	33,099		$	22,485
Equity Compensation		971			206
Temporary differences		138			113

Total deferred tax assets		34,208			22,804
Valuation allowance		(34,208	)		(22,804	)

Net deferred tax assets	$	—		$	—

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2014

Selected Quarterly Financial Data (Unaudited)

Schedule of unaudited quarterly financial data

	2014
	March 31			June 30			September 30			December 31
	(in thousands, except share and per share data)
Operating expenses:
Research and development	$	5,400		$	6,528		$	7,174		$	6,200
General and administrative		2,490			2,726			2,526			3,180

Total operating expenses		7,890			9,254			9,700			9,380
Loss from operations:		(7,890	)		(9,254	)		(9,700	)		(9,380	)

Interest expense		—			(1	)		(135	)		(134	)
Change in fair value of warrant liability		—			—			—			—
Other income (expense), net		16			17			29			57

Net loss	$	(7,874	)	$	(9,238	)	$	(9,806	)	$	(9,457	)


Net loss per common share (basic and diluted)	$	(0.51	)	$	(0.60	)	$	(0.64	)	$	(0.49	)
Weighted-average shares outstanding (basic and diluted)		15,369,055			15,399,018			15,432,641			19,276,639

	2013
	March 31			June 30			September 30			December 31
Operating expenses:
Research and development	$	2,093		$	3,100		$	3,483		$	7,338
General and administrative		1,251			1,172			1,924			2,398

Total operating expenses		3,344			4,272			5,407			9,736
Loss from operations:		(3,344	)		(4,272	)		(5,407	)		(9,736	)

Interest expense		(828	)		(108	)		—			—
Change in fair value of warrant liability		(42	)		(2,545	)		—			—
Other income (expense), net		(25	)		4			169			46

Net loss	$	(4,239	)	$	(6,921	)	$	(5,238	)	$	(9,690	)


Net loss per common share (basic and diluted)	$	(12.24	)	$	(19.82	)	$	(0.34	)	$	(0.63	)
Weighted-average shares outstanding (basic and diluted)		346,478			349,170			15,253,704			15,340,713

The Company and Basis of Presentation (Details) $ / shares in Units, $ in Millions					12 Months Ended
	Jul. 11, 2013 USD ($) $ / shares shares	Jul. 11, 2013 shares	Jul. 02, 2013 USD ($) $ / shares shares	Jun. 11, 2013 $ / shares	Dec. 31, 2014 $ / shares	Dec. 31, 2013 $ / shares shares	Jun. 30, 2014 shares	Dec. 31, 2012 $ / shares	Dec. 31, 2010 $ / shares
Reverse Stock Split
Reverse stock split ratio of outstanding common stock				0.1431	0.1431
Par value of common stock (in dollars per share) \| $ / shares				$ 0.001	$ 0.001	$ 0.001		$ 0.001	$ 0.001
Common stock \| Warrant
Initial Public Offering
Warrants exercisable into common stock (in shares)			277,690				8,230
Series A preferred stock
Initial Public Offering
Number of shares of convertible preferred stock converted into common stock						(57,598,092)
Series A-1 preferred stock
Initial Public Offering
Number of shares of convertible preferred stock converted into common stock						(6,750,000)
Initial Public Offering
Initial Public Offering
Original issue price (in dollars per share) \| $ / shares			$ 14.00
Net proceeds from the IPO, including proceeds from the exercise of the underwriters' over-allotment option \| $	$ 72.2
Initial Public Offering \| Common stock
Initial Public Offering
Common stock sold (in shares)			5,000,000
Number of shares of convertible preferred stock converted into common stock			9,210,999
Initial Public Offering \| Common stock \| Additional paid-in capital
Initial Public Offering
Reclassification of convertible preferred stock warrant liability to additional paid-in capital \| $			$ 2.9
Initial Public Offering \| Series A preferred stock
Initial Public Offering
Number of shares of convertible preferred stock converted into common stock			8,244,781
Initial Public Offering \| Series A-1 preferred stock
Initial Public Offering
Number of shares of convertible preferred stock converted into common stock			966,218
Over-allotment option
Initial Public Offering
Common stock sold (in shares)	750,000	750,000
Original issue price (in dollars per share) \| $ / shares	$ 14.00

Debt (Details) - USD ($)			1 Months Ended		4 Months Ended	12 Months Ended
Debt (Details) - USD ($)	Jul. 02, 2013	Feb. 28, 2013	Jun. 30, 2014	Feb. 28, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May 29, 2013	Apr. 19, 2013	Nov. 30, 2012	Sep. 30, 2012	Jan. 31, 2012	Dec. 31, 2011	Apr. 28, 2008
Debt
Deferred financing costs						$ 100,000
Series A preferred stock
Estimated future principal payments due under the Credit Facility
Conversion of convertible promissory notes into Series A preferred stock (in shares)							16,623,092
Preferred stock, shares issued					23,975,000			23,975,000						23,975,000
Share price of preferred stock (in dollars per share)										$ 1.00
Number of shares of preferred stock converted into shares of common stock							(57,598,092)
Series A-1 preferred stock
Estimated future principal payments due under the Credit Facility
Conversion of convertible promissory notes into Series A preferred stock (in shares)							6,750,000
Number of shares of preferred stock converted into shares of common stock							(6,750,000)
Warrant
Debt
Exercise price (in dollars per share)						$ 7.23
Series A preferred stock warrant
Debt
Warrants exercisable into stock (in shares)	1,940,000
Exercise price (in dollars per share)	$ 1.00
10% Convertible promissory notes \| Series A preferred stock
Estimated future principal payments due under the Credit Facility
Aggregate principal amount		$ 15,700,000		$ 15,700,000
Accrued interest		$ 900,000		$ 900,000
Conversion of convertible promissory notes into Series A preferred stock (in shares)		16,623,092		16,623,092
Conversion price (in dollars per share)		$ 1.00		$ 1.00
Short term convertible notes issued January 2012
Debt
Interest rate (as a percent)													10.00%
Estimated future principal payments due under the Credit Facility
Aggregate principal amount													$ 6,000,000
Short term convertible notes issued September and November 2012
Debt
Interest rate (as a percent)											10.00%
Estimated future principal payments due under the Credit Facility
Aggregate principal amount											$ 9,700,000
Short term borrowings with related parties, net of debt discount											9,400,000
Short term convertible notes issued September and November 2012 \| Series A preferred stock warrant \| Series A preferred stock
Estimated future principal payments due under the Credit Facility
Aggregate purchase price of warrants					$ 9,700
Short term convertible notes issued September and November 2012 \| Series A preferred stock warrant \| Total
Estimated future principal payments due under the Credit Facility
Estimated fair value of warrants											$ 300,000
Short term convertible notes issued September 2012
Estimated future principal payments due under the Credit Facility
Fair value of beneficial conversion feature				$ 300,000
Short term convertible notes issued September 2012 \| Interest Expense.
Estimated future principal payments due under the Credit Facility
Amortization of debt discount and beneficial conversion						$ 200,000	$ 200,000	$ 100,000
Short term convertible notes issued September 2012 \| Warrant \| Total
Estimated future principal payments due under the Credit Facility
Estimated fair value of warrants												$ 100,000
Pfizer note
Debt
Interest rate (as a percent)															8.931%
Estimated future principal payments due under the Credit Facility
Aggregate principal amount															$ 5,000,000
Outstanding principal amount									$ 7,800,000
Accrued interest during period							$ 300,000	$ 600,000
Pfizer note \| Series A-1 preferred stock
Estimated future principal payments due under the Credit Facility
Preferred stock, shares issued									6,750,000
Share price of preferred stock (in dollars per share)									$ 1.1560
Number of shares of preferred stock converted into shares of common stock	966,218
Credit Facility
Debt
Maximum borrowing capacity						$ 20,000,000
Percentage of final payment equal to amount drawn under the Credit Facility						8.00%
Estimated future principal payments due under the Credit Facility
2015						$ 638,000
2016						1,604,000
2017						1,709,000
2018						1,049,000
Total						5,000,000
Interest expense						300,000
Interest payments						100,000
Term A Loan
Debt
Maximum borrowing capacity						$ 5,000,000
Period of consecutive equal monthly installments of principal and interest						36 months
Interest rate (as a percent)						6.40%
Term A Loan \| Warrant
Debt
Warrants exercisable into stock (in shares)			8,230
Exercise price (in dollars per share)			$ 15.19
Unamortized discount			$ 100,000
Term A Loan \| Secured promissory notes
Debt
Proceeds from issuance of debt			$ 5,000,000
Term B Loan
Debt
Maximum borrowing capacity						$ 15,000,000
Remaining borrowing capacity						$ 15,000,000
Interest rate (as a percent)						6.40%
Reference rate						three month LIBOR
Number of business days prior to funding of new term loan						3 days
Interest rate margin (as a percent)						6.17%

Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Jun. 30, 2014	Jul. 02, 2013	Nov. 30, 2012	Sep. 30, 2012
Warrants
(Loss)/gain recognized for change in the fair value of the warrant liability	$ (2,545)	$ (42)	$ (2,587)	$ 32
Warrant
Warrants
Exercise price (in dollars per share)					$ 7.23
Number of shares of common stock to be purchased against outstanding warrants					285,920
Warrant \| Total \| Short term convertible notes issued September 2012
Warrants
Estimated fair value									$ 100
Warrant \| Total \| Short term convertible notes issued November 2012
Warrants
Estimated fair value								$ 200
Series A preferred stock warrant
Warrants
Warrants exercisable into stock (in shares)							1,940,000
Exercise price (in dollars per share)							$ 1.00
Number of shares of common stock to be purchased against outstanding warrants					277,690
Series A preferred stock warrant \| Total \| Short term convertible notes issued September and November 2012
Warrants
Estimated fair value								$ 300
Common stock
Warrants
Exercise price (in dollars per share)						$ 15.19
Common stock \| Warrant
Warrants
Warrants exercisable into stock (in shares)						8,230	277,690
Fair value of warrants						$ 100
Share price of common stock (in dollars per share)							$ 6.99

Commitments and contingencies (Details)	1 Months Ended		12 Months Ended
Commitments and contingencies (Details)	May 31, 2014 USD ($) ft² item	Feb. 28, 2014	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Commitments and contingencies
Term period of lease		63 months
Operating lease period for monthly rent increasing in fixed monthly rent		12 months
Operating lease period after which monthly rent increase		3 months
Operating leases
Total			$ 552,000
Less than 1 Year			133,000
1-3 Years			251,000
3-5 Years			168,000
Total
Total			552,000
Less than 1 Year			133,000
1-3 Years			251,000
3-5 Years			168,000
Rent expense			$ 300,000	$ 300,000	$ 300,000
Third amendment to the operating lease agreement for laboratory facility in Plymouth, Michigan
Commitments and contingencies
Adjusted rentable laboratory space (in square feet) \| ft²	3,045
Adjusted proportionate share of landlord's expenses and taxes (as a percent)	7.40%
Number of terms which Company may exercise to renew lease \| item	1
Lease renewal term	3 years
Annual base rent under new lease agreement	$ 37,000

Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Other Accrued Liabilities
Accrued compensation	$ 313	$ 667
Accrued professional fees	167	210
Accrued franchise and property taxes	107	95
Accrued interest	104
Accrued other	144	115
Total other accrued liabilities	$ 835	$ 1,087

Investments (Details) - USD ($)	3 Months Ended								12 Months Ended
Investments (Details) - USD ($)	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash equivalents and investments
Gross Unrealized Gains	$ 4,000				$ 4,000				$ 4,000	$ 4,000
Gross Unrealized Losses	(63,000)				(7,000)				(63,000)	(7,000)
Total, Amortized Cost	56,960,000				26,422,000				56,960,000	26,422,000
Total, Estimated Fair Value	56,901,000				26,419,000				56,901,000	26,419,000
Other income (expense), net	57,000	$ 29,000	$ 17,000	$ 16,000	46,000	$ 169,000	$ 4,000	$ (25,000)	119,000	194,000	$ (84,000)
Reclassification out of accumulated other comprehensive income (loss)
Cash equivalents and investments
Other income (expense), net									0
Short-term investments. \| U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost	9,020,000				2,071,000				9,020,000	2,071,000
Gross Unrealized Gains	4,000								4,000
Investments, Estimated Fair Value	9,024,000				2,071,000				9,024,000	2,071,000
Short-term investments. \| U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	8,853,000				1,454,000				8,853,000	1,454,000
Gross Unrealized Losses	(8,000)								(8,000)
Investments, Estimated Fair Value	8,845,000				1,454,000				8,845,000	1,454,000
Long-term investments \| U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost	2,494,000				9,116,000				2,494,000	9,116,000
Gross Unrealized Gains					3,000					3,000
Gross Unrealized Losses	(5,000)				(2,000)				(5,000)	(2,000)
Investments, Estimated Fair Value	2,489,000				9,117,000				2,489,000	9,117,000
Long-term investments \| U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	31,454,000				8,187,000				31,454,000	8,187,000
Gross Unrealized Gains					1,000					1,000
Gross Unrealized Losses	(50,000)				(5,000)				(50,000)	(5,000)
Investments, Estimated Fair Value	31,404,000				8,183,000				31,404,000	8,183,000
Money market funds
Cash equivalents and investments
Cash equivalents, Estimated Fair Value	357,000				5,356,000				357,000	5,356,000
Certificates of deposit \| Short-term investments.
Cash equivalents and investments
Investments, Amortized Cost	2,934,000								2,934,000
Investments, Estimated Fair Value	2,934,000								2,934,000
Certificates of deposit \| Long-term investments
Cash equivalents and investments
Investments, Amortized Cost	1,848,000				238,000				1,848,000	238,000
Investments, Estimated Fair Value	$ 1,848,000				$ 238,000				$ 1,848,000	$ 238,000

Convertible Preferred Stock and Stockholders' Equity (Details) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended
	Jul. 02, 2013 $ / shares shares	Apr. 19, 2013 USD ($) $ / shares shares	Feb. 28, 2013 USD ($) $ / shares shares	Feb. 28, 2013 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) shares	May 29, 2013 USD ($) $ / shares shares	Nov. 30, 2012 USD ($)	Jan. 31, 2012 USD ($)	Apr. 28, 2008 USD ($)
Convertible preferred stock and stockholders' deficit
Proceeds from issuance of preferred stock, net of issuance costs \| $					$ 16,824
Pfizer note
Convertible preferred stock and stockholders' deficit
Interest rate (as a percent)									8.931%
Aggregate principal amount \| $									$ 5,000
Outstanding principal amount \| $						$ 7,800
Short term convertible notes issued January 2012
Convertible preferred stock and stockholders' deficit
Interest rate (as a percent)								10.00%
Aggregate principal amount \| $								$ 6,000
Short term convertible notes issued September and November 2012
Convertible preferred stock and stockholders' deficit
Interest rate (as a percent)							10.00%
Aggregate principal amount \| $							$ 9,700
Common stock \| Warrant
Convertible preferred stock and stockholders' deficit
Share price of preferred stock (in dollars per share) \| $ / shares	$ 6.99
Series A preferred stock
Convertible preferred stock and stockholders' deficit
Conversion of convertible promissory notes into Series A preferred stock (in shares)					16,623,092
Preferred stock, shares authorized		17,000,000
Share price of preferred stock (in dollars per share) \| $ / shares		$ 1.00
Proceeds from issuance of preferred stock, net of issuance costs \| $		$ 16,900
Stock issuance costs \| $		$ 100			$ (120)
Conversion rate		0.143
Number of shares of convertible preferred stock converted into common stock					(57,598,092)
Series A preferred stock \| 10% Convertible promissory notes
Convertible preferred stock and stockholders' deficit
Aggregate principal amount \| $			$ 15,700	$ 15,700
Accrued interest \| $			$ 900	$ 900
Conversion of convertible promissory notes into Series A preferred stock (in shares)			16,623,092	16,623,092
Conversion price (in dollars per share) \| $ / shares			$ 1.00	$ 1.00
Conversion rate			0.143	0.143
Series A-1 preferred stock
Convertible preferred stock and stockholders' deficit
Conversion of convertible promissory notes into Series A preferred stock (in shares)					6,750,000
Stock issuance costs \| $					$ 53
Number of shares of convertible preferred stock converted into common stock					(6,750,000)
Series A-1 preferred stock \| Pfizer note
Convertible preferred stock and stockholders' deficit
Preferred stock, shares authorized						6,750,000
Share price of preferred stock (in dollars per share) \| $ / shares						$ 1.1560
Conversion rate						0.143
Number of shares of convertible preferred stock converted into common stock	966,218
Initial Public Offering \| Common stock
Convertible preferred stock and stockholders' deficit
Number of shares of convertible preferred stock converted into common stock	9,210,999
Initial Public Offering \| Series A preferred stock
Convertible preferred stock and stockholders' deficit
Number of shares of convertible preferred stock converted into common stock	8,244,781
Initial Public Offering \| Series A-1 preferred stock
Convertible preferred stock and stockholders' deficit
Number of shares of convertible preferred stock converted into common stock	966,218

Stock Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jun. 25, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Options
Outstanding at the beginning of period (in shares)		1,401,101
Granted (in shares)		561,500
Forfeited or expired (vested and unvested) (in shares)		(125,052)
Exercised (in shares)		(107,963)
Outstanding at the end of the period (in shares)		1,729,586	1,401,101
Weighted-Average Price Per Share
Outstanding at the beginning of period (in dollars per share)		$ 9.59
Granted (in dollars per share)		15.03
Forfeited or expired (vested and unvested) (in dollars per share)		12.97
Exercised (in dollars per share)		4.38
Outstanding at the end of the period (in dollars per share)		$ 11.44	$ 9.59
Weighted-Average Remaining Contractual Term (Years)
Outstanding at the end of the period		8 years 5 months 5 days	8 years 11 months 12 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)		$ 50,155	$ 7,755
Information about the stock option plan
Number of Options, vested and expected to vest (in shares)		1,671,313
Number of Options, exercisable (in shares)		752,397
Weighted-Average Price Per Share, vested and expected to vest (in dollars per share)		$ 11.37
Weighted-Average Price Per Share, exercisable (in dollars per share)		$ 6.61
Weighted-Average Remaining Contractual Term, vested and expected to vest		8 years 4 months 28 days
Weighted-Average Remaining Contractual Term, exercisable		7 years 6 months 29 days
Aggregate Intrinsic Value, vested and expected to vest (in dollars)		$ 48,588
Aggregate Intrinsic Value, exercisable (in dollars)		25,452
Total intrinsic value of stock options exercised		1,400	$ 200	$ 100
Additional disclosures
Unrecognized compensation cost (in dollars)		$ 9,300
Weighted-average period over which remaining unrecognized compensation cost will be recognized		2 years 10 months 24 days
Weighted-average grant-date fair value (in dollars per share)		$ 10.15	$ 7.14	$ 1.33
Stock-based compensation expense		$ 3,700	$ 1,200	$ 100
Assumptions used to compute the share-based compensation costs for stock options granted to employees and non-employees
Risk-free interest rate (as a percent)		1.81%	1.45%	0.85%
Weighted-average expected life of options (years)		6 years 3 months 26 days	6 years 3 months 4 days	6 years 3 months
Volatility (as a percent)		75.00%	74.00%	80.00%
2013 Stock Option and Incentive Plan
Stock compensation
Shares reserved and approved for issuance	1,100,000
Shares reserved under previous plan and subsequently transferred to new plan	54,129
Percentage of increase in the number of shares reserved and available for issuance	2.50%
2008 Incentive Stock Option and Restricted Stock Plan
Stock compensation
Shares reserved under previous plan and subsequently transferred to new plan	54,129
Expiration period		10 years
Period from cessation of employment within which options expire if not exercised		90 days
Grant period of stock awards		10 years
Purchase price expressed as a percentage of fair value of shares on the date of grant		100.00%
Vesting percentage on the first anniversary of the option grant		25.00%
Period for which remainder of grant amount will vest on the first day of each calendar quarter		3 years

Income Taxes (Detail 2) - USD ($)	12 Months Ended
Income Taxes (Detail 2) - USD ($)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate
Federal income tax (benefit) at statutory rate	(34.00%)	(34.00%)	(34.00%)
Change in Tax Rate	2.10%
Permanent items	1.00%	4.90%	0.40%
Other	0.10%		(0.20%)
Change in valuation allowance	30.80%	29.10%	33.80%
Effective income tax rate	0.00%	0.00%	0.00%
Unrecognized tax benefits related to interest and penalties accrued	$ 0

Selected Quarterly Financial Data (Unaudited) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Expenses [Abstract]
Research and development	$ 6,200	$ 7,174	$ 6,528	$ 5,400	$ 7,338	$ 3,483	$ 3,100	$ 2,093	$ 25,302	$ 16,014	$ 7,998
General and administrative	3,180	2,526	2,726	2,490	2,398	1,924	1,172	1,251	10,922	6,745	2,206
Total operating expenses	9,380	9,700	9,254	7,890	9,736	5,407	4,272	3,344	36,224	22,759	10,204
Loss from operations	(9,380)	(9,700)	(9,254)	(7,890)	(9,736)	(5,407)	(4,272)	(3,344)	(36,224)	(22,759)	(10,204)
Interest expense.	(134)	(135)	(1)				(108)	(828)	(270)	(936)	(1,486)
Change in fair value of warrant liability							(2,545)	(42)		(2,587)	32
Other income (expense), net	57	29	17	16	46	169	4	(25)	119	194	(84)
Net loss	$ (9,457)	$ (9,806)	$ (9,238)	$ (7,874)	$ (9,690)	$ (5,238)	$ (6,921)	$ (4,239)	$ (36,375)	$ (26,088)	$ (11,742)
Net loss per common share (basic and diluted) (in dollars per share)	$ (0.49)	$ (0.64)	$ (0.60)	$ (0.51)	$ (0.63)	$ (0.34)	$ (19.82)	$ (12.24)	$ (2.22)	$ (3.31)	$ (36.31)
Weighted-average shares outstanding (basic and diluted) (in shares)	19,276,639	15,432,641	15,399,018	15,369,055	15,340,713	15,253,704	349,170	346,478	16,374,102	7,885,921	323,382

Condensed Statements of Cash Flows (Parenthetical) $ in Thousands	Dec. 31, 2014 USD ($)
10% Convertible promissory notes
Conversion of convertible promissory notes into preferred stock, accrued interest	$ 923
Pfizer note
Conversion of convertible promissory notes into preferred stock, accrued interest	$ 274

Convertible Preferred Stock and Stockholders' Equity	12 Months Ended
Convertible Preferred Stock and Stockholders' Equity	Dec. 31, 2014
Convertible Preferred Stock and Stockholders' Equity
Convertible Preferred Stock and Stockholders' Equity	10. Convertible Preferred Stock and Stockholders' Equity In January 2012 the Company issued $6.0 million of 10% convertible promissory notes to certain existing investors for cash. In September and November 2012, the Company issued an aggregate of $9.7 million of 10% convertible promissory notes to certain existing investors for cash. In February 2013, these convertible promissory notes, with an outstanding principal of $15.7 million and accrued interest of $0.9 million, were amended and then converted into 16,623,092 shares of Series A preferred stock, in accordance with their terms and at their conversion price of $1.00 per share, and following such conversion, the notes were cancelled. Each share of Series A preferred stock issued in the financing was convertible into 0.143 shares of common stock upon the closing of the Company's IPO. On April 19, 2013, the Company issued and sold an aggregate of 17,000,000 shares of Series A preferred stock at a price of $1.00 per share for proceeds of $16.9 million, which is net of issuance costs of $0.1 million, to funds affiliated with Longitude Capital and certain existing investors. Each share of Series A preferred stock issued in the financing was convertible into 0.143 shares of common stock upon the closing of the Company's IPO. On May 29, 2013, the Company entered into a stock purchase agreement with Pfizer Inc. and issued and sold 6,750,000 shares of Series A-1 preferred stock at a price of $1.1560 per share. The purchase price was paid through the cancellation of all outstanding indebtedness, including accrued interest, under the Pfizer convertible promissory note, which had an aggregate balance, including accrued interest, of $7.8 million as of May 29, 2013. Each share of Series A-1 preferred stock issued in the agreement was convertible into 0.143 shares of common stock upon the closing of the Company's IPO. Upon the closing of the Company's IPO on July 1, 2013, all of the outstanding shares of convertible preferred stock were converted into 9,210,999 shares of common stock. As of December 31, 2014, the Company did not have any convertible preferred stock issued or outstanding.

Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2014
Employee Benefit Plan
Employee Benefit Plan	12. Employee Benefit Plan During 2008, the Company adopted the Esperion Therapeutics, Inc. 401(k) Plan (the "401(k) Plan"), which qualifies as a deferred salary arrangement under Section 401(k) of the Internal Revenue Code. Under the 401(k) Plan, participating employees may defer a portion of their pretax earnings. The Company may, at its sole discretion, contribute for the benefit of eligible employees. There have been no Company contributions to the 401(k) Plan during 2014, 2013, or 2012.

License Agreement	12 Months Ended
License Agreement	Dec. 31, 2014
License Agreement
License Agreement	14. License Agreement In December 2011, the Company entered into a license agreement for certain U.S. and foreign patents and patent applications regarding new high-density lipoprotein therapies to treat cardiovascular disease in exchange for 2,862 shares of common stock, plus an issue fee of $50,000. The license agreement will expire in 2028, which is the date of the last to expire of the licensed patents. The Company recorded the common stock, which was valued at its fair value of $4,400, and the issue fee within general and administrative expenses in the statements of operations. The license agreement provides for a minimum annual payment of $50,000 for any years in which a milestone is not achieved, fully creditable against any earned royalties per calendar year. In addition, the Company is also contractually obligated to issue up to an aggregate of 11,451 shares of common stock upon various milestones set forth in the agreement. Milestone achievement payments are due within 30 days of the milestone achievement. No milestones have been achieved to date under the license agreement. Additionally, the agreement provides for the Company to reimburse the patent holder for certain patent costs during the term of the agreement. The Company recognized expense associated with this license agreement of $50,000 during each of the years ended December 31, 2014, 2013 and 2012, in general and administrative expenses.

Summary of Significant Accounting Policies (Details)	12 Months Ended
Summary of Significant Accounting Policies (Details)	Dec. 31, 2014 USD ($) item	Dec. 31, 2008 USD ($)
Segment Information
Number of operating segments \| item	1
Impairment of Long-Lived Assets
Other impairment losses	$ 0
In-Process Research and Development
Acquired in-process research and development		$ 100,000
Property and equipment \| Minimum
Property and equipment, net
Estimated useful lives	3 years
Property and equipment \| Maximum
Property and equipment, net
Estimated useful lives	10 years

The Company and Basis of Presentation (Details 2) - shares				12 Months Ended
	Jul. 11, 2013	Jul. 11, 2013	Jul. 02, 2013	Dec. 31, 2013
Movement in Company's capitalization
Balance (in shares)	396,414
Balance (in shares)	15,357,413	15,357,413	14,607,413	15,357,413
Series A preferred stock
Movement in Company's capitalization
Conversion of preferred stock into common stock upon closing of IPO (in shares)				(57,598,092)
Series A-1 preferred stock
Movement in Company's capitalization
Conversion of preferred stock into common stock upon closing of IPO (in shares)				(6,750,000)
Initial Public Offering \| Series A preferred stock
Movement in Company's capitalization
Conversion of preferred stock into common stock upon closing of IPO (in shares)			8,244,781
Initial Public Offering \| Series A-1 preferred stock
Movement in Company's capitalization
Conversion of preferred stock into common stock upon closing of IPO (in shares)			966,218
Initial Public Offering \| Common stock
Movement in Company's capitalization
Conversion of preferred stock into common stock upon closing of IPO (in shares)			9,210,999
Common stock sold (in shares)			5,000,000
Over-allotment option
Movement in Company's capitalization
Common stock sold (in shares)	750,000	750,000

Commitments and contingencies (Details 2) - License agreement.	12 Months Ended
	Dec. 31, 2014 USD ($) shares
License agreement
Milestone minimum annual payment \| $	$ 50,000
Maximum
License agreement
Number of shares of common stock to be issued upon meeting various future milestones \| shares	11,451

Property and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property and Equipment
Property and equipment, gross	$ 1,183	$ 769
Less accumulated depreciation and amortization	403	688
Property and equipment, net	780	81
Depreciation expense	160	71	$ 139
Lab equipment
Property and Equipment
Property and equipment, gross	519	511
Computer equipment
Property and Equipment
Property and equipment, gross	110	100
Software
Property and Equipment
Property and equipment, gross	74	119
Furniture and fixtures
Property and Equipment
Property and equipment, gross	320	11
Leasehold improvements
Property and Equipment
Property and equipment, gross	158	21
Assets in Progress
Property and Equipment
Property and equipment, gross	$ 2	$ 7

Fair Value Measurements (Details) - USD ($)	12 Months Ended
Fair Value Measurements (Details) - USD ($)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets:
Total, Estimated Fair Value	$ 56,901,000	$ 26,419,000
Transfer of assets between levels	0	0
Transfer of liabilities between levels		0	$ 0
U.S. treasury notes
Assets:
Available for sale securities		11,188,000
U.S. government agency securities
Assets:
Available for sale securities		9,637,000
Certificates of deposit
Assets:
Available for sale securities		238,000
Level 1 \| U.S. treasury notes
Assets:
Available for sale securities		11,188,000
Level 1 \| Certificates of deposit
Assets:
Available for sale securities		238,000
Level 2
Assets:
Total, Estimated Fair Value		9,637,000
Level 2 \| U.S. government agency securities
Assets:
Available for sale securities		9,637,000
Recurring fair value measurement \| Level 1
Assets:
Money market fund	357,000	5,356,000
Total, Estimated Fair Value	16,652,000	16,782,000
Recurring fair value measurement \| Level 1 \| U.S. treasury notes
Assets:
Available for sale securities	11,513,000
Recurring fair value measurement \| Level 1 \| Certificates of deposit
Assets:
Available for sale securities	4,782,000
Recurring fair value measurement \| Level 2
Assets:
Total, Estimated Fair Value	40,249,000
Recurring fair value measurement \| Level 2 \| U.S. government agency securities
Assets:
Available for sale securities	40,249,000
Recurring fair value measurement \| Total
Assets:
Money market fund	357,000	5,356,000
Total, Estimated Fair Value	56,901,000	$ 26,419,000
Recurring fair value measurement \| Total \| U.S. treasury notes
Assets:
Available for sale securities	11,513,000
Recurring fair value measurement \| Total \| U.S. government agency securities
Assets:
Available for sale securities	40,249,000
Recurring fair value measurement \| Total \| Certificates of deposit
Assets:
Available for sale securities	$ 4,782,000

Employee Benefit Plan (Details) - USD ($)	12 Months Ended
Employee Benefit Plan (Details) - USD ($)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Benefit Plan
Contributions to the 401(k) Plan	$ 0	$ 0	$ 0

Income Taxes (Details) - USD ($)	12 Months Ended
Income Taxes (Details) - USD ($)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes
Provision for income taxes	$ 0	$ 0	$ 0
Deferred tax assets, before valuation allowance	34,208,000	22,804,000	14,400,000
Net operating loss carryforwards
NOLs related to excess tax benefits	500,000
Federal
Net operating loss carryforwards
Net operating loss carryforwards	95,100,000	62,300,000	40,500,000
State
Net operating loss carryforwards
Net operating loss carryforwards	$ 16,600,000	$ 33,100,000	$ 11,300,000

Income Taxes (Detail 3) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Federal and state operating loss carryforwards	$ 33,099	$ 22,485
Equity Compensation	971	206
Temporary differences	138	113
Total deferred tax assets	34,208	22,804	$ 14,400
Valuation allowance	$ (34,208)	$ (22,804)

Net Loss Per Common Share (Details)		12 Months Ended
Net Loss Per Common Share (Details)	Jun. 11, 2013	Dec. 31, 2014 shares	Dec. 31, 2013 shares
Net Loss Per Common Share
Reverse stock split ratio of shares outstanding	0.1431	0.1431
Net Loss Per Common Share
Total potential dilutive shares		2,025,057	1,695,494
Warrant
Net Loss Per Common Share
Total potential dilutive shares		285,920	277,690
Common shares under option
Net Loss Per Common Share
Total potential dilutive shares		1,729,586	1,401,101
Unvested restricted stock
Net Loss Per Common Share
Total potential dilutive shares		9,551	16,703

Label	Element	Value
Common Stock [Member]
Common Stock, Shares, Issued	us-gaap_CommonStockSharesIssued	20,352,876