View Filing Data

Document and Entity Information - $ / shares		3 Months Ended
Document and Entity Information - $ / shares	May 01, 2015	Mar. 31, 2015
Document and Entity Information
Entity Registrant Name		Esperion Therapeutics, Inc.
Entity Central Index Key		0001434868
Document Type		10-Q
Document Period End Date		Mar. 31, 2015
Amendment Flag		false
Current Fiscal Year End Date		--12-31
Entity Current Reporting Status		Yes
Entity Filer Category		Accelerated Filer
Entity Common Stock, Shares Outstanding	22,459,588
Document Fiscal Year Focus		2015
Document Fiscal Period Focus		Q1
Entity Listing, Par Value Per Share	$ 0.001

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 208,641	$ 85,038
Short-term investments	69,467	20,803
Prepaid clinical development costs	1,053	366
Other prepaid and current assets	665	492
Total current assets	279,826	106,699
Property and equipment, net	728	780
Intangible assets	56	56
Long-term investments	44,611	35,741
Total assets	325,221	143,276
Current liabilities:
Accounts payable	2,899	2,040
Current portion of long-term debt	1,030	638
Accrued clinical development costs	1,958	1,978
Other accrued liabilities	1,052	835
Total current liabilities	6,939	5,491
Long-term debt, net of discount and issuance costs	3,855	4,231
Total liabilities	10,794	9,722
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized as of March 31, 2015 and December 31, 2014; no shares issued or outstanding at March 31, 2015 and December 31, 2014
Common stock, $0.001 par value; 120,000,000 shares authorized as of March 31, 2015 and December 31, 2014; 22,455,338 shares issued and 22,447,575 outstanding at March 31, 2015 and 20,352,876 shares issued and 20,343,325 outstanding at December 31, 2014	22	20
Additional paid-in capital	430,348	238,031
Accumulated other comprehensive loss	(39)	(59)
Accumulated deficit	(115,904)	(104,438)
Total stockholders' equity	314,427	133,554
Total liabilities and stockholders' equity	$ 325,221	$ 143,276

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2015	Dec. 31, 2014
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	22,455,338	20,352,876
Common stock, shares outstanding	22,447,575	20,343,325

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating expenses:
Research and development	$ 7,390	$ 5,400
General and administrative	4,035	2,490
Total operating expenses	11,425	7,890
Loss from operations	(11,425)	(7,890)
Interest expense.	(134)
Other income, net	93	16
Net loss	$ (11,466)	$ (7,874)
Net loss per common share (basic and diluted) (in dollars per share)	$ (0.56)	$ (0.51)
Weighted-average shares outstanding (basic and diluted)	20,589,293	15,369,055
Other comprehensive income:
Unrealized gain on investments	$ 20	$ 3
Total comprehensive loss	$ (11,446)	$ (7,871)

Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net loss	$ (11,466)	$ (7,874)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	59	12
Amortization of debt discount and beneficial conversion	8
Amortization of debt issuance costs	8
Amortization of premiums and discounts on investments	27	53
Stock-based compensation expense	2,072	741
Loss related to assets held for sale		6
Loss on sale of assets		11
Changes in assets and liabilities:
Prepaids and other assets	(860)	(1,028)
Accounts payable	813	(159)
Other accrued liabilities	76	(866)
Net cash used in operating activities	(9,263)	(9,104)
Investing activities
Purchases of investments	(70,354)	(3,000)
Proceeds from sales/maturities of investments	12,813	4,426
Purchase of property and equipment	(7)	(273)
Net cash used in investing activities	(57,548)	1,153
Financing activities
Proceeds from issuance of common stock, net of issuance costs	190,150
Proceeds from exercise of common stock options	264	52
Net cash provided by financing activities	190,414	52
Net increase (decrease) in cash and cash equivalents	123,603	(7,899)
Cash and cash equivalents at beginning of period	85,038	56,537
Cash and cash equivalents at end of period	208,641	$ 48,638
Supplemental disclosure of cash flow information:
Offering costs not yet paid	$ 173

The Company and Basis of Presentation	3 Months Ended
The Company and Basis of Presentation	Mar. 31, 2015
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 patients with hypercholesterolemia and other cardiometabolic risk markers. ETC-1002, or bempedoic acid, the Company’s lead product candidate, is a first-in-class, orally available, once-daily small molecule designed to lower elevated LDL-cholesterol levels and avoid the side effects associated with currently available LDL-cholesterol lowering therapies. ETC-1002 is being developed for patients with primary hyperlipidemia and mixed dyslipidemia. The Company’s two completed Phase 2b clinical studies build upon a successful and comprehensive Phase 1 and Phase 2 clinical development program for ETC-1002. The Company plans to hold an End-of-Phase 2 meeting with the Food and Drug Administration (“FDA”) in the third quarter of 2015 and expects to initiate its Phase 3 program for ETC-1002 by the end of 2015. 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. On March 24, 2015, the Company completed an underwritten public offering of 2,012,500 shares of common stock, including 262,500 shares sold pursuant to the full exercise of an over-allotment option granted to the underwriters. All the shares were offered by the Company at a price to the public of $100.00 per share. The aggregate net proceeds received by the Company from the offering were $190.0 million, net of underwriting discounts and commissions and expenses payable by the Company. Basis of Presentation The accompanying condensed financial statements are unaudited and were prepared by the Company in accordance with generally accepted accounting principles in the United States of America (“GAAP”). In the opinion of management, the Company has made all adjustments, which include only normal recurring adjustments necessary for a fair statement of the Company’s financial position and results of operations for the interim periods presented. Certain information and disclosures normally included in the annual financial statements prepared in accordance with GAAP have been condensed or omitted. These condensed interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. The results of operations for the interim periods are not necessarily indicative of the results to be expected for a full year, any other interim periods or any future year or period.

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2015
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies In April 2015, the Financial Accounting Standards Board issued Accounting Standards Update 2015-03 which simplifies the presentation of debt issuance costs by requiring that debt issuance costs related to a recognized debt liability be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts, rather than as a deferred charge. The recognition and measurement guidance for debt issuance costs are not affected by the amendment. The Company early-adopted the amendment effective January 1, 2015, which resulted in a change in the balance sheet presentation of net debt; in prior period disclosures the debt issuance costs related to the Company’s debt liability were presented on the balance sheet as deferred charges within “Other prepaid and current assets”. Upon adoption of the amended guidance, the debt issuance costs associated with the Company’s debt liability are presented on the balance sheet as a direct deduction from the carrying amount of the debt liability. Within the March 31, 2015, and December 31, 2014, balance sheets, “Long-term debt, net of discount and issuance costs” includes $0.1 million and $0.1 million, respectively, of debt issuance costs. There have been no other material changes to the significant accounting policies previously disclosed in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2014.

Debt

3 Months Ended

Mar. 31, 2015

Debt

Debt

3. Debt

In June 2014, the Company entered into a loan and security agreement (the “Credit Facility”) with Oxford Finance LLC which provided for an initial borrowing of $5.0 million under the term loan (the “Term A Loan”) and additional borrowings of $15.0 million (the “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. Upon achieving positive clinical development results in March 2015, the remaining $15.0 million under the Term B Loan became available to be drawn down, at the Company’s sole discretion, until March 31, 2015. The Company did not elect to draw down the Term B Loan as of March 31, 2015. The 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 the 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. The Term A Loan bears interest at an annual rate of 6.40%. In addition, a final payment equal to 8.0% of the Term A Loan is due upon the earlier of the maturity date or prepayment of the term loan. 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 the Term A Loan, the Company issued a 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 the Term A Loan. In addition, deferred financing costs of $0.1 million included in long-term debt on the condensed balance sheet as of March 31, 2015, are amortized to interest expense using the effective-interest method over the same term. As of March 31, 2015, 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)
2015	638
2016	1,604
2017	1,709
2018	1,049
Total	$	5,000

During the three months ended March 31, 2015, the Company recognized $0.1 million of interest expense and made cash interest payments of $0.1 million related to the Credit Facility.

Warrants	3 Months Ended
Warrants	Mar. 31, 2015
Warrants
Warrants	4. Warrants In connection with the Credit Facility entered into in June 2014, the Company issued a warrant to purchase 8,230 shares of common stock at an exercise price of $15.19. The warrant will terminate on the earlier of June 30, 2019, and the closing of a merger or consolidation transaction in which the Company is not the surviving entity. The warrant was recorded at fair value of $0.1 million to additional-paid-in-capital in accordance with Accounting Standards Codification (“ASC”) 815-10 based upon the allocation of the debt proceeds. The Company estimated the fair value of the warrant using a Black-Scholes option-pricing model, which is based, in part, upon subjective assumptions including but not limited to stock price volatility, the expected life of the warrant, the risk-free interest rate and the fair value of the common stock underlying the warrant. The Company estimates the volatility of its stock based on public company peer group historical volatility that is in line with the expected remaining life of the warrant. The risk-free interest rate is based on the U.S. Treasury zero-coupon bond for a maturity similar to the expected remaining life of the warrant. The expected remaining life of the warrant is assumed to be equivalent to its remaining contractual term. In connection with its various convertible note financing transactions entered into prior to its initial public offering in July 2013, (the “IPO”), the Company issued warrants to purchase shares of preferred stock which had provisions where the underlying issuance was contingently redeemable based on events outside the Company’s control and were recorded as a liability in accordance with ASC 480-10. The warrants were classified as liabilities and were recorded on the Company’s balance sheet at fair value on the date of issuance and marked-to-market on each subsequent reporting period, with the fair value changes recognized in the statement of operations. Subsequent to the pricing of its IPO, the Company estimated the fair values of the warrants at each reporting period using a Black-Scholes option-pricing model, which is based, in part, upon subjective assumptions including but not limited to stock price volatility, the expected life of the warrants, the risk free interest rate and the fair value of the common stock underlying the warrants. The Company estimates the volatility of its stock based on public company peer group historical volatility that is in line with the expected remaining life of the warrants. The risk free interest rate is based on the U.S. Treasury zero-coupon bond for a maturity similar to the expected remaining life of the warrants. The expected remaining life of the warrants is assumed to be equivalent to their remaining contractual term. Prior to the pricing of the IPO, a Monte Carlo valuation model was utilized to estimate the fair value of the warrants based on the probability and timing of future financings. Upon the closing of the Company’s IPO, all warrants exercisable for 1,940,000 shares of Series A preferred stock, at an exercise price of $1.00 per share (unadjusted for stock splits), were automatically converted into warrants exercisable for 277,690 shares of common stock, at an exercise price of $6.99 per share. As a result, the Company concluded the warrants outstanding no longer met the criteria to be classified as liabilities and were reclassified to additional paid-in capital at fair value on the date of reclassification. During the three months ended March 31, 2015, 29,330 warrants were net exercised for 25,445 shares of the Company’s common stock. The remaining 248,360 warrants outstanding as of March 31, 2015, expire in February 2018. As of March 31, 2015, the Company had warrants outstanding that were exercisable for a total of 256,590 shares of common stock at a weighted-average exercise price of $7.25 per share.

Investments

3 Months Ended

Mar. 31, 2015

Investments

Investments

5. Investments

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

	March 31, 2015
	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	5,083		—		(1		)	5,082
U.S. treasury notes	5,505		3		—			5,508
U.S. government agency securities	58,898		2		(23		)	58,877
Long-term investments:
Certificates of deposit	5,741		—		—			5,741
U.S. treasury notes	2,495		1		—			2,496
U.S. government agency securities	36,395		2		(23		)	36,374
Total	$	114,474	$	8	$	(47	)	$	114,435

	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

At March 31, 2015, and 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 loss to other income in the Statements of Operations during the three months ended March 31, 2015.

Fair Value Measurements

3 Months Ended

Mar. 31, 2015

Fair Value Measurements

Fair Value Measurements

6. 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)
March 31, 2015
Assets:
Money market funds	$	357	$	357	$	—	$	—
Available-for-sale securities:
Certificates of deposit	10,823		10,823		—		—
U.S. treasury notes	8,004		8,004		—		—
U.S. government agency securities	95,251		—		95,251		—
Total assets at fair value	$	114,435	$	19,184	$	95,251	$	—
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	$	—

There were no transfers between Levels 1, 2 or 3 during the three months ended March 31, 2015.

- 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

3 Months Ended

Mar. 31, 2015

Stock Compensation

Stock Compensation

7. Stock Compensation

2013 Stock Option and Incentive Plan

The following table summarizes the activity relating to the Company’s options to purchase common stock for the three months ended March 31, 2015:

	Number of Options		Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
						(in thousands)
Outstanding at December 31, 2014	1,729,586		$	11.44	8.43	$	50,155
Granted	611,600		$	58.79
Forfeited or expired	(10,988	)	$	16.30
Exercised	(64,517	)	$	4.10
Outstanding at March 31, 2015	2,265,681		$	24.41	8.80	$	156,460

The following table summarizes information about the Company’s stock option plan as of March 31, 2015:

	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 March 31, 2015	2,174,929	$	23.95	8.78	$	151,135
Exercisable at March 31, 2015	749,429	$	7.52	7.87	$	63,760

As of March 31, 2015, there was approximately $30.1 million of unrecognized compensation cost related to unvested options, adjusted for forfeitures, which will be recognized over a weighted-average period of approximately 3.5 years.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2015
Income Taxes
Income Taxes	8. Income Taxes There was no provision for income taxes for the three months ended March 31, 2015 and 2014 because the Company has incurred operating losses since inception. At March 31, 2015, the Company 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, a full valuation allowance has been applied against the net deferred tax assets.

Net Loss Per Common Share

3 Months Ended

Mar. 31, 2015

Net Loss Per Common Share

Net Loss Per Common Share

9. Net Loss Per Common Share

Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, warrants for common stock, stock options and unvested restricted stock are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

The shares outstanding at the end of the respective periods presented below were excluded from the calculation of diluted net loss per share due to their anti-dilutive effect:

	March 31, 2015	December 31, 2014

Warrants for common stock	256,590	285,920
Common shares under option	2,265,681	1,729,586
Unvested restricted stock	7,763	9,551
Total potential dilutive shares	2,530,034	2,025,057

The Company and Basis of Presentation (Policies)	3 Months Ended
The Company and Basis of Presentation (Policies)	Mar. 31, 2015
The Company and Basis of Presentation
Basis of Presentation	Basis of Presentation The accompanying condensed financial statements are unaudited and were prepared by the Company in accordance with generally accepted accounting principles in the United States of America (“GAAP”). In the opinion of management, the Company has made all adjustments, which include only normal recurring adjustments necessary for a fair statement of the Company’s financial position and results of operations for the interim periods presented. Certain information and disclosures normally included in the annual financial statements prepared in accordance with GAAP have been condensed or omitted. These condensed interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. The results of operations for the interim periods are not necessarily indicative of the results to be expected for a full year, any other interim periods or any future year or period.

Debt (Tables)

3 Months Ended

Mar. 31, 2015

Debt

Schedule of estimated future principal payments due

Years Ending December 31,	(in thousands)
2015	638
2016	1,604
2017	1,709
2018	1,049
Total	$	5,000

Investments (Tables)

3 Months Ended

Mar. 31, 2015

Investments

Summary of the Company's cash equivalents and investments

	March 31, 2015
	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	5,083		—		(1		)	5,082
U.S. treasury notes	5,505		3		—			5,508
U.S. government agency securities	58,898		2		(23		)	58,877
Long-term investments:
Certificates of deposit	5,741		—		—			5,741
U.S. treasury notes	2,495		1		—			2,496
U.S. government agency securities	36,395		2		(23		)	36,374
Total	$	114,474	$	8	$	(47	)	$	114,435

	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

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

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)
March 31, 2015
Assets:
Money market funds	$	357	$	357	$	—	$	—
Available-for-sale securities:
Certificates of deposit	10,823		10,823		—		—
U.S. treasury notes	8,004		8,004		—		—
U.S. government agency securities	95,251		—		95,251		—
Total assets at fair value	$	114,435	$	19,184	$	95,251	$	—
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	$	—

Stock Compensation (Tables)

3 Months Ended

Mar. 31, 2015

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, 2014	1,729,586		$	11.44	8.43	$	50,155
Granted	611,600		$	58.79
Forfeited or expired	(10,988	)	$	16.30
Exercised	(64,517	)	$	4.10
Outstanding at March 31, 2015	2,265,681		$	24.41	8.80	$	156,460

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 March 31, 2015	2,174,929	$	23.95	8.78	$	151,135
Exercisable at March 31, 2015	749,429	$	7.52	7.87	$	63,760

Net Loss Per Common Share (Tables)

3 Months Ended

Mar. 31, 2015

Net Loss Per Common Share

Schedule of anti-dilutive securities excluded from the calculation of diluted net loss per share

	March 31, 2015	December 31, 2014

Warrants for common stock	256,590	285,920
Common shares under option	2,265,681	1,729,586
Unvested restricted stock	7,763	9,551
Total potential dilutive shares	2,530,034	2,025,057

The Company and Basis of Presentation (Details) $ / shares in Units, $ in Millions	Mar. 24, 2015 USD ($) $ / shares shares
Initial Public Offering
Initial Public Offering
Original issue price (in dollars per share) \| $ / shares	$ 100.00
Net proceeds from the IPO, including proceeds from the exercise of the underwriters' over-allotment option \| $	$ 190.0
Initial Public Offering \| Common stock
Initial Public Offering
Common stock sold (in shares)	2,012,500
Over-allotment option \| Common stock
Initial Public Offering
Common stock sold (in shares)	262,500

Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Debt
Debt issuance costs	$ 0.1	$ 0.1

Debt (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
Debt (Details) $ / shares in Units, $ in Thousands	Jun. 30, 2014 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) item $ / shares	Jul. 02, 2013 $ / shares shares
Warrant
Debt
Exercise price (in dollars per share) \| $ / shares		$ 7.25
Series A preferred stock warrant
Debt
Warrants exercisable into stock (in shares) \| shares			1,940,000
Exercise price (in dollars per share) \| $ / shares			$ 1.00
Credit Facility
Debt
Maximum borrowing capacity		$ 20,000
Percentage of final payment equal to amount drawn under the Credit Facility		8.00%
Number of financial covenants associated to the Credit Facility \| item		0
Deferred financing costs		$ 100
Estimated future principal payments due under the Credit Facility
2015		1,604
2016		1,709
2017		1,049
Total		5,000
2014		638
Interest expense		100
Interest payments		100
Term A Loan
Debt
Maximum borrowing capacity		$ 5,000
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) \| shares	8,230
Exercise price (in dollars per share) \| $ / shares	$ 15.19
Unamortized discount	$ 100	$ 100
Deferred financing costs		100
Term A Loan \| Secured promissory notes
Debt
Proceeds from issuance of debt	$ 5,000
Term B Loan
Debt
Maximum borrowing capacity		15,000
Remaining borrowing capacity		$ 15,000

Warrants (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2015	Jun. 30, 2014	Jul. 02, 2013
Warrant
Warrants
Exercise price (in dollars per share)	$ 7.25
Warrants exercised	29,330
Number of shares of common stock to be purchased against outstanding warrants	256,590
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	248,360
Common stock
Warrants
Exercise price (in dollars per share)		$ 15.19
Common stock \| Warrant
Warrants
Warrants exercisable into stock (in shares)	25,445	8,230	277,690
Fair value of warrants		$ 0.1
Share price of common stock (in dollars per share)			$ 6.99

Investments (Details) - USD ($) $ in Thousands	3 Months Ended
Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Cash equivalents and investments
Gross Unrealized Gains	$ 8		$ 4
Gross Unrealized Losses	(47)		(63)
Total, Amortized Cost	114,474		56,960
Total, Estimated Fair Value	114,435		56,901
Other income (expense), net	93	$ 16
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	5,505		9,020
Gross Unrealized Gains	3		4
Investments, Estimated Fair Value	5,508		9,024
Short-term investments. \| U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	58,898		8,853
Gross Unrealized Gains	2
Gross Unrealized Losses	(23)		(8)
Investments, Estimated Fair Value	58,877		8,845
Long-term investments \| U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost	2,495		2,494
Gross Unrealized Gains	1
Gross Unrealized Losses			(5)
Investments, Estimated Fair Value	2,496		2,489
Long-term investments \| U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	36,395		31,454
Gross Unrealized Gains	2
Gross Unrealized Losses	(23)		(50)
Investments, Estimated Fair Value	36,374		31,404
Money market funds
Cash equivalents and investments
Cash equivalents, Estimated Fair Value	357		357
Investments, Amortized Cost	357		357
Certificates of deposit \| Short-term investments.
Cash equivalents and investments
Investments, Amortized Cost	5,083		2,934
Gross Unrealized Losses	(1)
Investments, Estimated Fair Value	5,082		2,934
Certificates of deposit \| Long-term investments
Cash equivalents and investments
Investments, Amortized Cost	5,741		1,848
Investments, Estimated Fair Value	$ 5,741		$ 1,848

Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Assets:
Total, Estimated Fair Value	$ 114,435	$ 56,901
Transfer of assets between levels	0
Recurring fair value measurement \| Level 1
Assets:
Money market fund	357	357
Total, Estimated Fair Value	19,184	16,652
Recurring fair value measurement \| Level 1 \| U.S. treasury notes
Assets:
Available for sale securities	8,004	11,513
Recurring fair value measurement \| Level 1 \| Certificates of deposit
Assets:
Available for sale securities	10,823	4,782
Recurring fair value measurement \| Level 2
Assets:
Total, Estimated Fair Value	95,251	40,249
Recurring fair value measurement \| Level 2 \| U.S. government agency securities
Assets:
Available for sale securities	95,251	40,249
Recurring fair value measurement \| Total
Assets:
Money market fund	357	357
Total, Estimated Fair Value	114,435	56,901
Recurring fair value measurement \| Total \| U.S. treasury notes
Assets:
Available for sale securities	8,004	11,513
Recurring fair value measurement \| Total \| U.S. government agency securities
Assets:
Available for sale securities	95,251	40,249
Recurring fair value measurement \| Total \| Certificates of deposit
Assets:
Available for sale securities	$ 10,823	$ 4,782

Stock Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Number of Options
Outstanding at the beginning of period (in shares)	1,729,586
Granted (in shares)	611,600
Forfeited or expired (vested and unvested) (in shares)	(10,988)
Exercised (in shares)	(64,517)
Outstanding at the end of the period (in shares)	2,265,681	1,729,586
Weighted-Average Price Per Share
Outstanding at the beginning of period (in dollars per share)	$ 11.44
Granted (in dollars per share)	58.79
Forfeited or expired (vested and unvested) (in dollars per share)	16.30
Exercised (in dollars per share)	4.10
Outstanding at the end of the period (in dollars per share)	$ 24.41	$ 11.44
Weighted-Average Remaining Contractual Term (Years)
Outstanding at the end of the period	8 years 9 months 18 days	8 years 5 months 5 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 156,460	$ 50,155
Information about the stock option plan
Number of Options, vested and expected to vest (in shares)	2,174,929
Number of Options, exercisable (in shares)	749,429
Weighted-Average Price Per Share, vested and expected to vest (in dollars per share)	$ 23.95
Weighted-Average Price Per Share, exercisable (in dollars per share)	$ 7.52
Weighted-Average Remaining Contractual Term, vested and expected to vest	8 years 9 months 11 days
Weighted-Average Remaining Contractual Term, exercisable	7 years 10 months 13 days
Aggregate Intrinsic Value, vested and expected to vest (in dollars)	$ 151,135
Aggregate Intrinsic Value, exercisable (in dollars)	63,760
Additional disclosures
Unrecognized compensation cost (in dollars)	$ 30,100
Weighted-average period over which remaining unrecognized compensation cost will be recognized	3 years 6 months

Income Taxes (Details) - USD ($)	3 Months Ended
Income Taxes (Details) - USD ($)	Mar. 31, 2015	Mar. 31, 2014
Income Taxes
Provision for income taxes	$ 0	$ 0

Net Loss Per Common Share (Details) - shares	3 Months Ended
Net Loss Per Common Share (Details) - shares	Mar. 31, 2015	Dec. 31, 2014
Net Loss Per Common Share
Total potential dilutive shares	2,530,034	2,025,057
Warrant
Net Loss Per Common Share
Total potential dilutive shares	256,590	285,920
Common shares under option
Net Loss Per Common Share
Total potential dilutive shares	2,265,681	1,729,586
Unvested restricted stock
Net Loss Per Common Share
Total potential dilutive shares	7,763	9,551