Esperion Therapeutics (ESPR) 10-K 28 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 01, 2019	Jun. 29, 2018
Document and Entity Information
Entity Registrant Name	Esperion Therapeutics, Inc.
Entity Central Index Key	1,434,868
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 978
Entity Common Stock, Shares Outstanding		26,824,859
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 36,973	$ 34,468
Short-term investments	99,050	165,731
Prepaid clinical development costs	5,275	2,072
Other prepaid and current assets	1,334	1,653
Total current assets	142,632	203,924
Property and equipment, net	520	435
Intangible assets	56	56
Long-term investments	243	73,420
Total assets	143,451	277,835
Current liabilities:
Accounts payable	44,893	20,375
Current portion of long-term debt		1,045
Accrued clinical development costs	16,039	10,506
Other accrued liabilities	3,401	1,218
Total current liabilities	64,333	33,144
Total liabilities	64,333	33,144
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, 2018 and December 31, 2017
Common stock, $0.001 par value; 120,000,000 shares authorized as of December 31, 2018 and December 31, 2017; 26,824,859 shares issued and outstanding at December 31, 2018 and 26,304,669 shares issued and outstanding at December 31, 2017	27	26
Additional paid-in capital	677,511	641,801
Accumulated other comprehensive loss	(319)	(845)
Accumulated deficit	(598,101)	(396,291)
Total stockholders' equity	79,118	244,691
Total liabilities and stockholders' equity	$ 143,451	$ 277,835

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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	26,824,859	26,304,669
Common stock, shares outstanding	26,824,859	26,304,669

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 171,488	$ 147,603	$ 57,868
General and administrative	33,097	21,379	18,282
Total operating expenses	204,585	168,982	76,150
Loss from operations	(204,585)	(168,982)	(76,150)
Other income, net	2,775	1,994	1,172
Net loss	$ (201,810)	$ (166,988)	$ (74,978)
Net loss per common share (basic and diluted) (in dollars per share)	$ (7.54)	$ (6.98)	$ (3.33)
Weighted-average shares outstanding (basic and diluted)	26,754,308	23,933,273	22,544,475
Other comprehensive gain (loss):
Unrealized gain (loss) on investments	$ 526	$ (673)	$ 310
Total comprehensive loss	$ (201,284)	$ (167,661)	$ (74,668)

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2015	$ 23	$ 441,940	$ (154,222)	$ (482)	$ 287,259
Balance (in shares) at Dec. 31, 2015	22,518,907
Increase (Decrease) in Stockholders' Equity
Early exercise of stock options and vesting of restricted stock		9			9
Exercise of stock options		45			45
Exercise of stock options (in shares)	27,757
Vesting of restricted stock options (in shares)	8,749
Stock-based compensation		15,957			15,957
Other comprehensive gain (loss)				310	310
Net loss			(74,978)		(74,978)
Balance at Dec. 31, 2016	$ 23	457,951	(229,200)	(172)	228,602
Balance (in shares) at Dec. 31, 2016	22,555,413
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standard 2016-09		103	(103)
Issuance of common stock from public offering, net of issuance costs	$ 3	163,975			163,978
Issuance of common stock from public offering, net of issuance costs (in shares)	3,565,000
Exercise of stock options		1,167			1,167
Exercise of stock options (in shares)	115,483
Exercise of warrants (in shares)	62,525
Vesting of restricted stock options (in shares)	6,248
Stock-based compensation		18,605			18,605
Other comprehensive gain (loss)				(673)	(673)
Net loss			(166,988)		(166,988)
Balance at Dec. 31, 2017	$ 26	641,801	(396,291)	(845)	$ 244,691
Balance (in shares) at Dec. 31, 2017	26,304,669				26,304,669
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 1	11,742			$ 11,743
Exercise of stock options (in shares)	356,809				356,809
Exercise of warrants (in shares)	159,944
Vesting of restricted stock options (in shares)	3,437
Stock-based compensation		23,968			$ 23,968
Other comprehensive gain (loss)				526	526
Net loss			(201,810)		(201,810)
Balance at Dec. 31, 2018	$ 27	$ 677,511	$ (598,101)	$ (319)	$ 79,118
Balance (in shares) at Dec. 31, 2018	26,824,859				26,824,859

Statements of Stockholders' E_2

Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Common Stock
Stock issuance costs paid and offering costs not yet paid	$ 226

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (201,810)	$ (166,988)	$ (74,978)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	265	258	252
Amortization (accretion) of premiums and discounts on investments	(217)	334	1,014
Stock-based compensation expense	23,968	18,605	15,957
Changes in assets and liabilities:
Prepaids and other assets	(2,884)	(1,731)	139
Accounts payable	24,446	15,758	3,888
Other accrued liabilities	7,594	2,462	5,998
Net cash used in operating activities	(148,638)	(131,302)	(47,730)
Investing activities
Purchases of investments	(25,481)	(219,577)	(197,230)
Proceeds from sales/maturities of investments	166,081	183,743	207,442
Purchase of property and equipment	(151)	(19)	(94)
Net cash provided by (used in) investing activities	140,449	(35,853)	10,118
Financing activities
Proceeds from issuance of common stock, net of issuance costs		164,000
Proceeds from exercise of common stock options	11,743	1,167	45
Payments on long-term debt	(1,049)	(1,709)	(1,604)
Net cash provided by (used in) financing activities	10,694	163,458	(1,559)
Net increase (decrease) in cash and cash equivalents	2,505	(3,697)	(39,171)
Cash and cash equivalents at beginning of period	34,468	38,165	77,336
Cash and cash equivalents at end of period	36,973	34,468	$ 38,165
Supplemental disclosure of cash flow information:
Purchase of property and equipment not yet paid	$ 199
Offering costs not yet paid		$ 22

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2018
The Company and Basis of Presentation
The Company and Basis of Presentation	1. The Company and Basis of Presentation The Company is the Lipid Management Company, a late-stage pharmaceutical company focused on developing and commercializing complementary, cost-effective, convenient, once-daily, oral therapies for the treatment of patients with elevated low density lipoprotein cholesterol ("LDL-C"). Through scientific and clinical excellence, and a deep understanding of cholesterol biology, the experienced Lipid Management Team at Esperion is committed to developing new LDL-C lowering therapies that will make a substantial impact on reducing global cardiovascular disease ("CVD"); the leading cause of death around the world. Bempedoic acid and the Company's lead product candidate, the bempedoic acid / ezetimibe combination tablet, are targeted therapies that have been shown to significantly lower elevated LDL-C levels in patients with hypercholesterolemia, including patients inadequately treated with current lipid-modifying therapies. The completed clinical development program for an LDL-C lowering indication for the bempedoic acid / ezetimibe combination tablet consisted of a single pivotal Phase 3 clinical study (1002FDC-053) in patients with hypercholesterolemia and with atherosclerotic cardiovascular disease ("ASCVD") and/or heterozygous familial hypercholesterolemia ("HeFH"), including high CVD risk primary prevention patients, whose LDL-C is not adequately controlled despite receiving maximally tolerated lipid-modifying background therapy. 1002FDC-053 initiated in November 2017, fully enrolled 382 patients in March 2018, and the Company reported top-line results in August 2018. The completed global pivotal Phase 3 clinical development program for an LDL-C lowering indication for bempedoic acid consisted of four clinical studies in 3,621 high CVD risk patients with hypercholesterolemia and ASCVD and/or HeFH, or who are high CVD risk primary prevention, on optimized background lipid-modifying therapy and with elevated levels of LDL-C. These patients are on two distinct types of background lipid-modifying therapy: 1) patients on their maximally tolerated statin therapy, and 2) patients who are only able to tolerate less than the lowest approved daily starting dose of a statin, and can be considered stain intolerant. In March 2018, the Company reported top-line results from the first of the Phase 3 studies, Study 4 (1002-048). In May 2018, the Company reported top-line results from the 52-week long-term safety study, Study 1 (1002-040), and from Study 3 (1002-046). In October 2018, the Company reported top-line results from Study 2 (1002-047). On February 20, 2019, the Company submitted the new drug application (“NDA”) for bempedoic acid and on February 26, 2019, the Company submitted the NDA for the bempedoic acid / ezetimibe combination tablet to the Food and Drug Administration (“FDA”) for LDL-C lowering indications. In addition, the European Medicines Agency (“EMA”) completed formal validation of the Marketing Authorization Applications (“MAAs”) for bempedoic acid and the bempedoic acid / ezetimibe combination tablet for LDL-C lowering indications. The MAAs for bempedoic acid and the bempedoic acid / ezetimibe combination tablet were submitted to the EMA on February 11, 2019. The Company is also conducting a global cardiovascular outcomes trial ("CVOT")—known as Cholesterol Lowering via BEmpedoic Acid, an ACL-inhibiting Regimen (CLEAR) Outcomes, for bempedoic acid in 12,604 patients with hypercholesterolemia and high CVD risk and who can be considered statin intolerant. The Company initiated the CLEAR Outcomes CVOT in December 2016 and expects the study to be fully enrolled in 2019, and intends to use positive results from this CVOT to support submissions for a CV risk reduction indication in the U.S. and Europe by 2022. 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. While management believes current cash resources and future cash received from the Company’s collaboration agreement with Daiichi Sankyo Europe GmbH (“DSE”), entered into on January 2, 2019, will fund operations for the foreseeable future, management may continue to fund operations and advance the development of the Company’s product candidates through a combination of collaborations with third parties, strategic alliances, licensing arrangements, debt financings, royalty-based financings, and private and public and equity offerings or through other sources. 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. Follow On Offerings On August 15, 2017, the Company completed an underwritten public offering of 3,100,000 shares of common stock. The Company also granted the underwriters a 30-day option to purchase up to 465,000 additional shares of its common stock which was exercised in full in September 2017. All the shares were offered by the Company at a price to the public of $49.00 per share. The aggregate net proceeds received by the Company from the offering were $164.0 million, net of underwriting discounts and commissions and expenses payable by the Company.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
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 accordance with generally accepted accounting principles in the United States 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. 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, net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income, 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 LDL-C. 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. No impairment losses have been recorded through December 31, 2018. 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 clinical activities, nonclinical activities, 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. Accrued Clinical Development Costs Outside research costs are a component of research and development expense. These expenses include fees paid to clinical 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 a tax benefit from its 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 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. In accordance with the adoption of Accounting Standards Update (“ASU”) 2016-09 on January 1, 2017, the Company accounts for forfeitures as they occur. Prior to January 1, 2017, under the provisions of ASC 718, the Company was 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 were 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 January 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-01 which includes provisions to accounting for equity investments, financial liabilities under the fair value option, and presentation and disclosure requirements for financial instruments. The updated guidance requires equity investments with determinable fair values to be measured at fair value with changes in fair value recognized in income. Equity investments without determinable fair values are to be measured at cost, less any impairment determined to be other than temporary. The Company adopted ASU 2016-01 effective January 1, 2018. The adoption of the ASU did not have a material impact to the Company’s balance sheets, statements of operations or statements of cash flows. In February 2016, the FASB issued ASU 2016-02, which was amended by subsequent updates (collectively the “lease standard” or “ASC 842”), and is intended to improve financial reporting about leasing transactions. The updated guidance will require a lessee to recognize assets and liabilities for leases with lease terms of more than twelve months. The standard is effective for public companies for fiscal years beginning after December 15, 2018, and interim periods within those years. ASC 842 requires companies to use a modified retrospective approach to each lease that existed at the date of the initial application. Further, companies must elect whether the initial date of application is the beginning of the earliest comparative period presented in the financial statements or the beginning of the period of adoption, in which case companies would not restate comparative periods. The Company will adopt this guidance on January 1, 2019, and has chosen not to restate comparative periods and will recognize any cumulative adjustment to retained earnings on the date of adoption. The Company is finalizing the evaluation of the impact of ASC 842, and expects to recognize approximately $1.0 million to $1.3 million of lease assets and lease liabilities on the Company’s balance sheets as of January 1, 2019, primarily related to the lease agreement for the Company’s principal executive office. The final impact of ASC 842 will depend on the Company’s lease commitments on the adoption date and subsequent reporting date. The Company does not believe the adoption of this standard will have a material impact on the Company’s statements of operations or statements of cash flows. In May 2017, the FASB issued ASU 2017-09 which includes provisions to clarify when to account for a change to terms or conditions of a share-based payment award as a modification. Under the updated guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. The Company adopted ASU 2017-09 effective January 1, 2018. The adoption of the ASU did not have a material impact to the Company’s balance sheets, statements of operations or statements of cash flows. In August 2018, the FASB issued ASU 2018-15 which includes provisions to clarify customer's accounting for implementation costs incurred in a cloud computing arrangement. Under the updated guidance, a customer in a cloud computing arrangement that is a service contract should follow the internal-use software guidance to determine how to account for costs incurred in implementation. The updated guidance also requires certain classification on the balance sheets, statements of operations and statements of cash flows as well as additional quantitative and qualitative disclosures. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Early adoption is permitted and entities can choose to adopt the new guidance prospectively or retrospectively. The Company does not believe the adoption of this standard to have a material impact to the Company's balance sheets, statements of operations or statements of cash flows.

Debt

Debt	12 Months Ended
	Dec. 31, 2018
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 provided for borrowings of $5.0 million under the term loan (the “Term A Loan”). 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 secured promissory notes issued under the Credit Facility were due on July 1, 2018, and were collateralized by substantially all of the Company’s personal property, other than its intellectual property. The Company was obligated to make monthly, interest-only payments on the Term A Loan until July 1, 2015, and, thereafter, paid 36 consecutive, equal monthly installments of principal and interest from August 1, 2015, through July 1, 2018. The Term A Loan beared interest at an annual rate of 6.40%. In addition, a final payment equal to 8.0% of the Term A Loan was due upon the earlier of the maturity date or prepayment of the term loan. The Company recognized the final payment as interest expense using the effective interest method over the life of the Credit Facility. The Term A Loan was fully repaid in July 2018. 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 was amortized into interest expense using the effective interest method over the life of the Term A Loan. In addition, the Company incurred debt issuance costs of $0.1 million in connection with the borrowing of the Term A Loan. The debt issuance costs were capitalized and included in long-term debt on the condensed balance sheet at the inception of the Term A Loan, and were amortized to interest expense using the effective interest method over the same term. As of December 31, 2018, there was no remaining unamortized discount and debt issuance costs associated with the debt. During the years ended December 31, 2018, 2017 and 2016, the Company recognized less than $0.1 million, $0.2 million and $0.4 million of interest expense, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company made cash interest payments related to the Credit Facility of $0.4 million, which included the final payment equal to 8% of the Term A Loan, $0.1 million and $0.2 million, respectively.

Warrants

Warrants	12 Months Ended
	Dec. 31, 2018
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 ASC 815-10 based upon the allocation of the debt proceeds. 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. During the year ended December 31, 2018, the remaining 177,123 warrants were net exercised for 159,944 shares of the Company's common stock. During the year ended December 31, 2017, 71,237 warrants were net exercised for 62,525 shares of the Company's common stock. During the year ended December 31, 2015, 29,330 warrants were net exercised for 25,445 shares of the Company’s common stock. As of December 31, 2018, the Company had warrants outstanding that were exercisable for a total of 8,230 shares of common stock at a weighted-average exercise price of $15.19 per share.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
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. On July 6, 2018, the Company entered into the first amendment of the lease for the Company's principal executive office in Ann Arbor, Michigan. The amended lease is to increase the current 7,941 rentable square feet of office space by 11,471 rentable square feet, together with the right to use common areas and facilities in common with the landlord and other tenants. The term of the lease commences with respect to all of the space in the leased premises on the later to occur of (i) the date upon which landlord delivers the premises to the Company under the terms of the lease with the delivery conditions set forth in the lease satisfied and (ii) November 1, 2018 (the "Lease Commencement Date"). The term of the lease shall end 60 months after the Lease Commencement Date. Under the terms of the lease, following the first month (during which the base rent is $0) and the second month (during which the base rent is $15,990), the base rent, subject to certain adjustments, for the leased premises will start at approximately $19,412 per month, plus certain operating expenses and taxes, and shall increase on an annual basis and/or as otherwise provided in the lease agreement. In August 2015, the Company entered into an operating lease agreement to increase its office space and support its clinical development operations located in Ann Arbor, Michigan, commencing September 2015, with a term of 49 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 month of the lease. On May 14, 2018, the Company provided notice of early lease termination for its second Ann Arbor lease of 5,500 square feet to end its tenancy effective November 15, 2018. The total rent expense for the years ended December 31, 2018, 2017 and 2016, was approximately $0.3 million, $0.2 million, and $0.2 million, respectively. The following table summarizes the Company’s future minimum lease payments as of December 31, 2018: Less than More than Total 1 Year 1 - 3 Years 3 - 5 Years 5 Years (in thousands) Operating lease $ 1,169 $ 234 $ 719 $ 216 $ — Total $ 1,169 $ 234 $ 719 $ 216 $ — Legal Proceedings On January 12, 2016, a purported stockholder of the company filed a putative class action lawsuit in the United States District Court for the Eastern District of Michigan, against the Company and Tim Mayleben, captioned Kevin L. Dougherty v. Esperion Therapeutics, Inc., et al. (No. 16-cv-10089). The lawsuit alleges that the Company and Mr. Mayleben violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and SEC Rule 10b-5 by allegedly failing to disclose in an August 17, 2015, public statement that the FDA would require a cardiovascular outcomes trial before approving the Company’s lead product candidate. The lawsuit seeks, among other things, compensatory damages in connection with an allegedly inflated stock price between August 18, 2015, and September 28, 2015, as well as attorneys’ fees and costs. On May 20, 2016, an amended complaint was filed in the lawsuit and on July 5, 2016, the Company filed a motion to dismiss the amended complaint. On December 27, 2016, the court granted the Company’s motion to dismiss with prejudice and entered judgment in the Company’s favor. On January 24, 2017, the plaintiffs in this lawsuit filed a motion to alter or amend the judgment. In May 2017, the court denied the plaintiff’s motion to alter or amend the judgment. On June 19, 2017, the plaintiffs filed a notice of appeal to the Sixth Circuit Court of Appeals and on September 14, 2017, they filed their opening brief in support of the appeal. The appeal was fully briefed on December 7, 2017, and it was argued before the Sixth Circuit on March 15, 2018. On September 27, 2018, the Sixth Circuit issued an opinion in which it reversed the district court’s dismissal and remanded for further proceedings. On October 11, 2018, the Company filed a petition for rehearing en banc and, on October 23, 2018, the Sixth Circuit Court of Appeals directed plaintiffs to respond to that petition. On December 3, 2018, the Sixth Circuit denied the Company’s petition for en banc rehearing, and on December 11, 2018, the case was returned to the federal district court by mandate from the Sixth Circuit. On December 26, 2018, the Company filed an answer to the amended complaint. The Company is unable to predict the outcome of this matter and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome. On December 15, 2016, a purported stockholder of the Company filed a derivative lawsuit in the Court of Chancery of the State of Delaware against Tim Mayleben, Roger Newton, Mary McGowan, Nicole Vitullo, Dov Goldstein, Daniel Janney, Antonio Gotto Jr., Mark McGovern, Gilbert Omenn, Scott Braunstein, and Patrick Enright. The Company is named as a nominal defendant. The lawsuit alleges that the defendants breached their fiduciary duties to the Company when they made or approved improper statements on August 17, 2015, regarding the Company’s lead product candidate’s path to FDA approval, and failed to ensure that reliable systems of internal controls were in place at the Company. On February 8, 2019, the Company and defendants filed a motion to dismiss the derivative lawsuit. The lawsuit seeks, among other things, any damages sustained by the Company as a result of the defendants’ alleged breaches of fiduciary duties, including damages related to the above-referenced securities class action, an order directing the Company to take all necessary actions to reform and improve its corporate governance and internal procedures, restitution from the defendants, and attorneys’ fees and costs. The Company is unable to predict the outcome of this matter and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome. On May 7, 2018, a purported stockholder of the Company filed a putative class action lawsuit in the United States District Court for the Eastern District of Michigan, captioned Kevin Bailey v. Esperion Therapeutics, Inc., et al. (No. 18-cv-11438). An amended complaint was filed on October 22, 2018, against the Company and certain directors and officers. The amended complaint alleges violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and SEC Rule 10b-5 based on allegedly making false and misleading statements and omissions about the safety and tolerability of bempedoic acid, and specifically facts and circumstances surrounding the Phase 3 trial results for bempedoic acid that the Company announced on May 2, 2018. On November 13, 2018, the Company filed a motion to dismiss the amended complaint, and that motion was fully briefed on December 18, 2018. On February 19, 2019, the court granted the Company's motion to dismiss with prejudice and entered judgment in the Company's favor. The lawsuit seeks, among other things, compensatory damages in connection with an allegedly inflated stock price between February 22, 2017, and May 22, 2018, as well as attorneys’ fees and costs. The Company is unable to predict the ultimate outcome of this matter and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2018
Property and Equipment
Property and Equipment	6. Property and Equipment Property and equipment consist of the following: December 31, 2018 2017 (in thousands) Lab equipment $ 232 $ 232 Computer equipment 51 114 Software 205 206 Furniture and fixtures 719 568 Leasehold improvements 309 159 Subtotal 1,516 1,279 Less accumulated depreciation and amortization 996 844 Property and equipment, net $ 520 $ 435 Depreciation expense was $0.3 million, $0.3 million, and $0.3 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Other Accrued Liabilities

Other Accrued Liabilities	12 Months Ended
	Dec. 31, 2018
Other Accrued Liabilities
Other Accrued Liabilities	7. Other Accrued Liabilities Other accrued liabilities consist of the following: December 31, 2018 2017 (in thousands) Accrued compensation $ 1,833 $ 582 Accrued professional fees 1,228 153 Accrued franchise and property taxes 44 38 Accrued interest — 397 Accrued other 296 48 Total other accrued liabilities $ 3,401 $ 1,218

Investments

Investments	12 Months Ended
	Dec. 31, 2018
Investments
Investments	8. Investments The following table summarizes the Company’s cash equivalents and investments: December 31, 2018 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cost Gains Losses Value (in thousands) Cash equivalents: Money market funds $ 34,526 $ — $ — $ 34,526 Short-term investments: Certificates of deposit 3,873 — (7) 3,866 U.S. treasury notes 44,897 — (142) 44,755 U.S. government agency securities 50,598 — (169) 50,429 Long-term investments: Certificates of deposit 244 — (1) 243 Total $ 134,138 $ — $ (319) $ 133,819 December 31, 2017 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cost Gains Losses Value (in thousands) Cash equivalents: Money market funds $ 27,302 $ — $ — $ 27,302 U.S. treasury notes 2,999 — — 2,999 Short-term investments: Certificates of deposit 12,429 1 (13) 12,417 U.S treasury notes 97,537 — (225) 97,312 U.S. government agency securities 56,143 — (141) 56,002 Long-term investments: Certificates of deposit 3,863 — (10) 3,853 U.S. treasury notes 27,983 — (209) 27,774 U.S. government agency securities 42,041 — (248) 41,793 Total $ 270,297 $ 1 $ (846) $ 269,452 At December 31, 2018, 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. During the years ended December 31, 2018, 2017 and 2016, other income, net in the statements of operations includes interest income on available-for-sale investments of $2.6 million, $2.5 million and $2.6 million. Other income, net in the statements of operations includes income for the accretion of premiums and discounts on investments of $0.2 million during the year ended December 31, 2018 and expense for the amortization of premiums and discounts on investments of $0.3 million and $1.0 million during the years ended December 31, 2017 and 2016, respectively. There were no unrealized gains or losses on investments reclassified from accumulated other comprehensive loss to other income, net in the statements of operations during the year ended December 31, 2018.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
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, 2018 Assets: Money market funds $ 34,526 $ 34,526 $ — $ — Investments: Certificates of deposit 4,109 4,109 — — U.S. treasury notes 44,755 44,755 — — U.S. government agency securities 50,429 — 50,429 — Total assets at fair value $ 133,819 $ 83,390 $ 50,429 $ — December 31, 2017 Assets: Money market funds $ 27,302 $ 27,302 $ — $ — Available-for-sale securities: Certificates of deposit 16,270 16,270 — — U.S. treasury notes 128,085 128,085 — — U.S. government agency securities 97,795 — 97,795 — Total assets at fair value $ 269,452 $ 171,657 $ 97,795 $ — There were no transfers between Levels 1, 2 or 3 during the years ended December 31, 2018 or December 31, 2017.

Stock Compensation

Stock Compensation	12 Months Ended
	Dec. 31, 2018
Stock Compensation
Stock Compensation	10. Stock Compensation 2017 Inducement Equity Plan In May 2017, the Company's board of directors approved the 2017 Inducement Equity Plan (the "2017 Plan"). The number of shares of common stock available for awards under the 2017 Plan was set to 750,000, with any shares of common stock that are forfeited, cancelled, held back upon the exercise 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 common stock, or otherwise terminated (other than by exercise) under the 2017 Plan added back to the shares of common stock available for issuance under the 2017 Plan. The 2017 Plan provides for the granting of stock options, stock appreciation rights, restricted stock awards, restricted stock units ("RSUs"), unrestricted stock awards and dividend equivalent rights. 2013 Stock Option and Incentive Plan In May 2015, the Company’s stockholders approved the amended and restated 2013 Stock Option and Incentive Plan (as amended, the “2013 Plan”) which, among other things, increased the number of shares of common stock reserved for issuance thereunder. The number of shares of common stock available for awards under the 2013 Plan was increased by 923,622 shares from 2,051,378 shares to 2,975,000 shares, plus (i) shares of common stock that are forfeited, cancelled, held back upon the exercise 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 common stock or otherwise terminated (other than by exercise) under the 2013 Plan and the Company’s 2008 Incentive Stock Option and Restricted Stock Plan are added back to the shares of common stock available for issuance under the 2013 Plan, and (ii) on January 1, 2016, and each January 1, thereafter, the number of shares of common stock reserved and available for issuance under the 2013 Plan will be cumulatively increased by 2.5% of the number of shares of common stock outstanding on the immediately preceding December 31, or such lesser number of shares of common stock determined by the compensation committee.The 2013 Plan provides for the granting of stock options, stock appreciation rights, restricted stock awards, RSUs, unrestricted stock awards, cash-based awards, performance share awards and dividend equivalent rights. 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, restricted stock awards or nonqualified stock options. 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. The Company incurs stock-based compensation expense related to stock options and RSUs. The fair value of RSUs is determined by the closing market price of the Company's common stock on the date of grant. The fair value of stock options is calculated using a Black-Scholes option-pricing model. 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. In accordance with the adoption of ASU 2016-09, effective January 1, 2017, the Company accounts for forfeitures as they occur. Prior to January 1, 2017, under the provisions of ASC 718, the Company was 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 were accounted for prospectively. Under the 2017 Plan, 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, 2018: Weighted-Average Weighted-Average Remaining Number of Exercise Price Contractual Aggregate Options Per Share Term (Years) Intrinsic Value (in thousands) Outstanding at December 31, 2017 4,159,151 $ 28.13 7.39 $ 165,385 Granted 1,890,177 $ 56.63 Forfeited or cancelled (vested and unvested) (388,796) $ 41.18 Exercised (356,809) $ 32.91 Outstanding at December 31, 2018 5,303,723 $ 37.01 7.42 $ 83,473 The following table summarizes information about the Company’s stock option plan as of December 31, 2018: Weighted-Average Weighted-Average Remaining Number of Exercise Price Contractual Aggregate Options Per Share Term (Years) Intrinsic Value (in thousands) Vested and expected to vest at December 31, 2018 5,303,723 $ 37.01 7.42 $ Exercisable at December 31, 2018 2,866,429 $ 28.82 6.04 $ The total intrinsic value of stock options exercised during the years ended December 31, 2018, 2017 and 2016, was $12.1 million, $4.0 million and $0.4 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 each of the three years ending December 31, 2018, using the Black-Scholes option-pricing model: Year ended December 31, 2018 2017 2016 Risk-free interest rate 2.75 % 2.04 % 1.47 % Dividend yield — — — Weighted-average expected life of options (years) 6.19 6.22 Volatility 72 % 73 % 71 % 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 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, 2018, 2017 and 2016, were $37.56, $15.99 and $9.78, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company recognized stock‑based compensation expense related to stock options of $23.4 million, $18.2 million and $15.6 million, respectively. As of December 31, 2018, there was approximately $66.4 million of unrecognized compensation cost related to unvested options, which will be recognized over a weighted‑average period of approximately 3.2 years. The following table summarizes the activity relating to the Company’s RSUs for the year ended December 31, 2018: Number of Weighted-Average RSUs Fair Value Per Share Outstanding and unvested at December 31, 2017 10,003 $ 57.54 Granted 37,600 $ 66.32 Forfeited or expired (6,691) $ 54.16 Vested (3,437) $ 57.54 Outstanding and unvested at December 31, 2018 37,475 $ 66.96 During the years ended December 31, 2018, 2017 and 2016, the Company recognized approximately $0.6 million, $0.4 million and $0.4 million, respectively, of stock-based compensation expense recognized related to RSUs. As of December 31, 2018, there was approximately $2.0 million of unrecognized stock-based compensation expense related to unvested RSUs, which will be recognized over a weighted-average period of approximately 3.1 years.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2018
Employee Benefit Plan
Employee Benefit Plan	11. 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. Company contributions to the 401(k) Plan during the years ended December 31, 2018, 2017 and 2016, were $0.3 million, $0.3 million and $0.2 million, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Taxes
Income Taxes	12. Income Taxes There was no provision for income taxes for the years ended December 31, 2018, 2017 and 2016, because the Company has incurred operating losses since inception. At December 31, 2018, 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. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (“TCJA”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. Tax from a worldwide to a territorial system, and potential additional limitations on deductions related to interest expense and executive compensation. The Company recorded a reduction to its gross deferred tax assets of $50.4 million in 2017, the period in which the legislation was enacted. The reduction in the Company’s gross deferred tax assets was fully offset by an equal reduction in the Company’s valuation allowance, resulting in no additional net income tax expense from the tax law change. The Company concluded on SAB 118 and finalized its reduction to gross deferred tax assets during 2018. As the gross reduction of the deferred tax assets were offset by a full valuation allowance, no net adjustment was required from the Company’s previous provisional estimate during 2018. On January 1, 2017, upon the Company’s adoption of ASU 2016-09, the Company recognized approximately $4.5 million of deferred tax assets that were not previously recognized on the Company’s balance sheet under the prior accounting guidance. The increase in the deferred tax assets was fully offset by an increase in the Company’s valuation allowance. As of December 31, 2018, 2017 and 2016, the Company had deferred tax assets, before valuation allowance, of approximately $152.2 million, $99.8 million and $75.3 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, 2018, 2017 and 2016, the Company had federal net operating loss (“NOL”) carryforwards of approximately $539.2 million, $347.4 million and $196.4 million, respectively. The federal NOL carryforwards will expire at various dates beginning in 2028, if not utilized. The Company filed certain amended state tax returns for tax years 2012-2015 during 2017 that resulted in increasing the Company’s state NOL carryforward. As of December 31, 2018, 2017 and 2016, the Company had state NOL carryforwards of approximately $526.6 million, $327.8 million and $18.1 million, respectively. The state NOL carryforwards will expire at various dates beginning in 2022, if not utilized. A reconciliation of the U.S. statutory income tax rate to the Company’s effective tax rate is as follows: December 31, 2018 2017 2016 Federal income tax (benefit) at statutory rate (21.0) % (34.0) % (34.0) % Change in tax rate 0.0 % 29.6 % 0.1 % Permanent items (0.5) % 0.1 % 0.9 % Other 0.5 % (0.9) % 0.2 % Amended Tax Returns 0.0 % (4.5) % 0.0 % Change in valuation allowance 21.0 % 9.7 % 32.8 % 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, 2018, 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, 2018 2017 (in thousands) Deferred tax assets: Federal and state operating loss carryforwards $ 138,299 $ 88,637 Equity compensation 13,542 10,809 Temporary differences 341 402 Total deferred tax assets 152,182 99,848 Valuation allowance (152,182) (99,848) Net deferred tax assets $ — $ —

Net Loss Per Common Share

Net Loss Per Common Share	12 Months Ended
	Dec. 31, 2018
Net Loss Per Common Share
Net Loss Per Common Share	13. 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 and RSUs 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: December 31, December 31, December 31, 2018 2017 2016 Warrants for common stock 8,230 185,353 256,590 Common shares under option 5,303,723 4,159,151 3,255,987 Unvested RSUs 37,475 10,003 16,251 Total potential dilutive shares 5,349,428 4,354,507 3,528,828

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Data (Unaudited)
Selected Quarterly Financial Data (Unaudited)	14. Selected Quarterly Financial Data (Unaudited) The following table summarizes the unaudited quarterly financial data for the last two years: 2018 March 31 June 30 September 30 December 31 (in thousands, except share and per share data) Operating expenses: Research and development $ 40,940 $ 39,524 $ 41,551 $ 49,473 General and administrative 5,954 6,956 9,011 11,176 Total operating expenses 46,894 46,480 50,562 60,649 Loss from operations: (46,894) (46,480) (50,562) (60,649) Other income, net 764 750 651 610 Net loss $ (46,130) $ (45,730) $ (49,911) $ (60,039) Net loss per common share (basic and diluted) $ (1.73) $ (1.71) $ (1.86) $ (2.24) Weighted-average shares outstanding (basic and diluted) 26,605,189 26,786,796 26,804,026 26,818,331 2017 March 31 June 30 September 30 December 31 (in thousands, except share and per share data) Operating expenses: Research and development $ 35,860 $ 38,248 $ 40,056 $ 33,439 General and administrative 5,029 5,412 5,681 5,257 Total operating expenses 40,889 43,660 45,737 38,696 Loss from operations: (40,889) (43,660) (45,737) (38,696) Other income, net 348 323 518 805 Net loss $ (40,541) $ (43,337) $ (45,219) $ (37,891) Net loss per common share (basic and diluted) (1) $ (1.80) $ (1.92) $ (1.86) $ (1.44) Weighted-average shares outstanding (basic and diluted) 22,563,152 22,591,326 24,311,844 26,222,397 (1) Due to the use of weighted average shares outstanding for each quarter for calculating net loss per common share, the sum of the quarterly net loss per common share amounts may not equal the net loss per common share amount for the full year.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events
Subsequent Events	15. Subsequent Events Collaboration and License Agreement with Daiichi Sankyo Europe GmbH On January 2, 2019, the Company entered into a License and Collaboration Agreement (the “Agreement”) with Daiichi Sankyo Europe GmbH (“DSE”). Pursuant to the Agreement, the Company granted DSE exclusive commercialization rights to bempedoic acid and the bempedoic acid / ezetimibe combination tablet in the European Economic Area and Switzerland (the “DSE Territory”). DSE will be responsible for commercialization in the DSE Territory. The Company will be responsible for clinical development, regulatory and manufacturing activities for the licensed products globally, including the DSE Territory. Pursuant to the agreement, the consideration consists of an upfront cash payment of $150 million as well as $150 million cash payment to the Company upon first commercial sales in the DSE Territory. The Company is also eligible to receive a substantial additional regulatory milestone payment upon the grant of the marketing authorization in the European Union for the CV risk reduction label, depending on the range of relative risk reduction in the CLEAR Outcomes study. In addition, the Company is eligible to receive additional sales milestone payments. Finally, the Company will receive tiered fifteen percent (15%) to twenty-five percent (25%) royalties on net DSE Territory sales.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with generally accepted accounting principles in the United States 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.
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, net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income, 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 LDL-C.
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. No impairment losses have been recorded through December 31, 2018.
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 clinical activities, nonclinical activities, 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.
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 clinical 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 a tax benefit from its 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 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. In accordance with the adoption of Accounting Standards Update (“ASU”) 2016-09 on January 1, 2017, the Company accounts for forfeitures as they occur. Prior to January 1, 2017, under the provisions of ASC 718, the Company was 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 were 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	Recent Accounting Pronouncements In January 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-01 which includes provisions to accounting for equity investments, financial liabilities under the fair value option, and presentation and disclosure requirements for financial instruments. The updated guidance requires equity investments with determinable fair values to be measured at fair value with changes in fair value recognized in income. Equity investments without determinable fair values are to be measured at cost, less any impairment determined to be other than temporary. The Company adopted ASU 2016-01 effective January 1, 2018. The adoption of the ASU did not have a material impact to the Company’s balance sheets, statements of operations or statements of cash flows. In February 2016, the FASB issued ASU 2016-02, which was amended by subsequent updates (collectively the “lease standard” or “ASC 842”), and is intended to improve financial reporting about leasing transactions. The updated guidance will require a lessee to recognize assets and liabilities for leases with lease terms of more than twelve months. The standard is effective for public companies for fiscal years beginning after December 15, 2018, and interim periods within those years. ASC 842 requires companies to use a modified retrospective approach to each lease that existed at the date of the initial application. Further, companies must elect whether the initial date of application is the beginning of the earliest comparative period presented in the financial statements or the beginning of the period of adoption, in which case companies would not restate comparative periods. The Company will adopt this guidance on January 1, 2019, and has chosen not to restate comparative periods and will recognize any cumulative adjustment to retained earnings on the date of adoption. The Company is finalizing the evaluation of the impact of ASC 842, and expects to recognize approximately $1.0 million to $1.3 million of lease assets and lease liabilities on the Company’s balance sheets as of January 1, 2019, primarily related to the lease agreement for the Company’s principal executive office. The final impact of ASC 842 will depend on the Company’s lease commitments on the adoption date and subsequent reporting date. The Company does not believe the adoption of this standard will have a material impact on the Company’s statements of operations or statements of cash flows. In May 2017, the FASB issued ASU 2017-09 which includes provisions to clarify when to account for a change to terms or conditions of a share-based payment award as a modification. Under the updated guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. The Company adopted ASU 2017-09 effective January 1, 2018. The adoption of the ASU did not have a material impact to the Company’s balance sheets, statements of operations or statements of cash flows. In August 2018, the FASB issued ASU 2018-15 which includes provisions to clarify customer's accounting for implementation costs incurred in a cloud computing arrangement. Under the updated guidance, a customer in a cloud computing arrangement that is a service contract should follow the internal-use software guidance to determine how to account for costs incurred in implementation. The updated guidance also requires certain classification on the balance sheets, statements of operations and statements of cash flows as well as additional quantitative and qualitative disclosures. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Early adoption is permitted and entities can choose to adopt the new guidance prospectively or retrospectively. The Company does not believe the adoption of this standard to have a material impact to the Company's balance sheets, statements of operations or statements of cash flows.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Summary of future minimum lease payments	The following table summarizes the Company’s future minimum lease payments as of December 31, 2018: Less than More than Total 1 Year 1 - 3 Years 3 - 5 Years 5 Years (in thousands) Operating lease $ 1,169 $ 234 $ 719 $ 216 $ — Total $ 1,169 $ 234 $ 719 $ 216 $ —

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property and Equipment
Schedule of property and equipment	December 31, 2018 2017 (in thousands) Lab equipment $ 232 $ 232 Computer equipment 51 114 Software 205 206 Furniture and fixtures 719 568 Leasehold improvements 309 159 Subtotal 1,516 1,279 Less accumulated depreciation and amortization 996 844 Property and equipment, net $ 520 $ 435

Other Accrued Liabilities (Tabl

Other Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Other Accrued Liabilities
Schedule of other accrued liabilities	December 31, 2018 2017 (in thousands) Accrued compensation $ 1,833 $ 582 Accrued professional fees 1,228 153 Accrued franchise and property taxes 44 38 Accrued interest — 397 Accrued other 296 48 Total other accrued liabilities $ 3,401 $ 1,218

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments
Summary of the Company's cash equivalents and investments	December 31, 2018 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cost Gains Losses Value (in thousands) Cash equivalents: Money market funds $ 34,526 $ — $ — $ 34,526 Short-term investments: Certificates of deposit 3,873 — (7) 3,866 U.S. treasury notes 44,897 — (142) 44,755 U.S. government agency securities 50,598 — (169) 50,429 Long-term investments: Certificates of deposit 244 — (1) 243 Total $ 134,138 $ — $ (319) $ 133,819 December 31, 2017 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cost Gains Losses Value (in thousands) Cash equivalents: Money market funds $ 27,302 $ — $ — $ 27,302 U.S. treasury notes 2,999 — — 2,999 Short-term investments: Certificates of deposit 12,429 1 (13) 12,417 U.S treasury notes 97,537 — (225) 97,312 U.S. government agency securities 56,143 — (141) 56,002 Long-term investments: Certificates of deposit 3,863 — (10) 3,853 U.S. treasury notes 27,983 — (209) 27,774 U.S. government agency securities 42,041 — (248) 41,793 Total $ 270,297 $ 1 $ (846) $ 269,452

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 Assets: Money market funds $ 34,526 $ 34,526 $ — $ — Investments: Certificates of deposit 4,109 4,109 — — U.S. treasury notes 44,755 44,755 — — U.S. government agency securities 50,429 — 50,429 — Total assets at fair value $ 133,819 $ 83,390 $ 50,429 $ — December 31, 2017 Assets: Money market funds $ 27,302 $ 27,302 $ — $ — Available-for-sale securities: Certificates of deposit 16,270 16,270 — — U.S. treasury notes 128,085 128,085 — — U.S. government agency securities 97,795 — 97,795 — Total assets at fair value $ 269,452 $ 171,657 $ 97,795 $ —

Stock Compensation (Tables)

Stock Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Stock Compensation
Summary of activity relating to the Company's options to purchase common stock	Weighted-Average Weighted-Average Remaining Number of Exercise Price Contractual Aggregate Options Per Share Term (Years) Intrinsic Value (in thousands) Outstanding at December 31, 2017 4,159,151 $ 28.13 7.39 $ 165,385 Granted 1,890,177 $ 56.63 Forfeited or cancelled (vested and unvested) (388,796) $ 41.18 Exercised (356,809) $ 32.91 Outstanding at December 31, 2018 5,303,723 $ 37.01 7.42 $ 83,473
Summary of information about the stock option plan	Weighted-Average Weighted-Average Remaining Number of Exercise Price Contractual Aggregate Options Per Share Term (Years) Intrinsic Value (in thousands) Vested and expected to vest at December 31, 2018 5,303,723 $ 37.01 7.42 $ Exercisable at December 31, 2018 2,866,429 $ 28.82 6.04 $
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, 2018 2017 2016 Risk-free interest rate 2.75 % 2.04 % 1.47 % Dividend yield — — — Weighted-average expected life of options (years) 6.19 6.22 Volatility 72 % 73 % 71 %
Summary of activity relating to the Company's RSUs	Number of Weighted-Average RSUs Fair Value Per Share Outstanding and unvested at December 31, 2017 10,003 $ 57.54 Granted 37,600 $ 66.32 Forfeited or expired (6,691) $ 54.16 Vested (3,437) $ 57.54 Outstanding and unvested at December 31, 2018 37,475 $ 66.96

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Taxes
Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate	December 31, 2018 2017 2016 Federal income tax (benefit) at statutory rate (21.0) % (34.0) % (34.0) % Change in tax rate 0.0 % 29.6 % 0.1 % Permanent items (0.5) % 0.1 % 0.9 % Other 0.5 % (0.9) % 0.2 % Amended Tax Returns 0.0 % (4.5) % 0.0 % Change in valuation allowance 21.0 % 9.7 % 32.8 % Effective income tax rate 0.0 % 0.0 % 0.0 %
Schedule of significant components of the Company's deferred tax assets	December 31, 2018 2017 (in thousands) Deferred tax assets: Federal and state operating loss carryforwards $ 138,299 $ 88,637 Equity compensation 13,542 10,809 Temporary differences 341 402 Total deferred tax assets 152,182 99,848 Valuation allowance (152,182) (99,848) Net deferred tax assets $ — $ —

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2018
Net Loss Per Common Share
Schedule of anti-dilutive securities excluded from the calculation of diluted net loss per share	December 31, December 31, December 31, 2018 2017 2016 Warrants for common stock 8,230 185,353 256,590 Common shares under option 5,303,723 4,159,151 3,255,987 Unvested RSUs 37,475 10,003 16,251 Total potential dilutive shares 5,349,428 4,354,507 3,528,828

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Data (Unaudited)
Schedule of unaudited quarterly financial data	2018 March 31 June 30 September 30 December 31 (in thousands, except share and per share data) Operating expenses: Research and development $ 40,940 $ 39,524 $ 41,551 $ 49,473 General and administrative 5,954 6,956 9,011 11,176 Total operating expenses 46,894 46,480 50,562 60,649 Loss from operations: (46,894) (46,480) (50,562) (60,649) Other income, net 764 750 651 610 Net loss $ (46,130) $ (45,730) $ (49,911) $ (60,039) Net loss per common share (basic and diluted) $ (1.73) $ (1.71) $ (1.86) $ (2.24) Weighted-average shares outstanding (basic and diluted) 26,605,189 26,786,796 26,804,026 26,818,331 2017 March 31 June 30 September 30 December 31 (in thousands, except share and per share data) Operating expenses: Research and development $ 35,860 $ 38,248 $ 40,056 $ 33,439 General and administrative 5,029 5,412 5,681 5,257 Total operating expenses 40,889 43,660 45,737 38,696 Loss from operations: (40,889) (43,660) (45,737) (38,696) Other income, net 348 323 518 805 Net loss $ (40,541) $ (43,337) $ (45,219) $ (37,891) Net loss per common share (basic and diluted) (1) $ (1.80) $ (1.92) $ (1.86) $ (1.44) Weighted-average shares outstanding (basic and diluted) 22,563,152 22,591,326 24,311,844 26,222,397 (1) Due to the use of weighted average shares outstanding for each quarter for calculating net loss per common share, the sum of the quarterly net loss per common share amounts may not equal the net loss per common share amount for the full year.

The Company and Basis of Pres_2

The Company and Basis of Presentation - Other (Details) - USD ($) $ / shares in Units, $ in Millions	Aug. 15, 2017	Sep. 30, 2017	Sep. 30, 2017
Follow-On Offering
Net proceeds from offerings, including proceeds from the exercise of the underwriters' over-allotment option			$ 164
Follow-On Offering
Follow-On Offering
Original issue price (in dollars per share)	$ 49	$ 49	$ 49
Follow-On Offering | Common stock
Follow-On Offering
Common stock sold (in shares)	3,100,000
Over-allotment option | Common stock
Follow-On Offering
Common stock sold (in shares)		465,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2018USD ($)segment
Segment Information
Number of operating segments | segment	1
Impairment of Long-Lived Assets
Impairment losses | $	$ 0
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

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - ASU 2016-02 - Restatement $ in Millions	Jan. 01, 2019USD ($)
Minimum
Recent Accounting Pronouncements
Lease assets	$ 1
Lease liabilities	1
Maximum
Recent Accounting Pronouncements
Lease assets	1.3
Lease liabilities	$ 1.3

Debt (Details)

Debt (Details) - USD ($) $ / shares in Units, $ in Thousands	Aug. 01, 2015	Jun. 30, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Warrants for common stock
Debt
Exercise price (in dollars per share)			$ 15.19
Credit Facility
Debt
Percentage of final payment equal to amount drawn under the Credit Facility		8.00%	8.00%
Interest expense				$ 200	$ 400
Interest payments			$ 400	$ 100	$ 200
Credit Facility | Maximum
Debt
Interest expense			$ 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%	6.40%
Debt issuance costs		$ 100
Unamortized discount and debt issuance costs			$ 0
Term A Loan | Warrants for common stock
Debt
Warrants exercisable into stock (in shares)		8,230
Exercise price (in dollars per share)		$ 15.19
Unamortized discount		$ 100
Term A Loan | Secured promissory notes
Debt
Proceeds from issuance of debt		$ 5,000

Warrants (Details)

Warrants (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Jun. 30, 2014	Jul. 01, 2013
Warrants for common stock
Warrants
Exercise price (in dollars per share)	$ 15.19
Warrants exercised	177,123	71,237	29,330
Number of shares of common stock to be purchased against outstanding warrants	8,230
Series A preferred stock warrant
Warrants
Warrants exercised/exercisable into stock (in shares)					1,940,000
Exercise price (in dollars per share)					$ 1
Common stock
Warrants
Exercise price (in dollars per share)				$ 15.19
Common stock | Warrants for common stock
Warrants
Warrants exercised/exercisable into stock (in shares)	159,944	62,525	25,445	8,230	277,690
Fair value of warrants				$ 0.1
Share price of common stock (in dollars per share)					$ 6.99

Commitments and Contingencies_2

Commitments and Contingencies (Details)	Jul. 06, 2018USD ($)ft²	May 14, 2018ft²	Aug. 31, 2015	Feb. 28, 2014	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Commitments and contingencies
Term period of lease			49 months	63 months
Operating lease period for monthly rent increasing in fixed monthly rent			12 months	12 months
Operating lease period after which monthly rent increase				3 months
Operating Lease Term			49 months	63 months
Operating leases
Total					$ 1,169,000
Less than 1 Year					234,000
1-3 Years					719,000
3-5 Years					216,000
Total
Total					1,169,000
Less than 1 Year					234,000
1-3 Years					719,000
3-5 Years					216,000
Rent expense					$ 300,000	$ 200,000	$ 200,000
Office space in Ann Arbor, Michigan
Commitments and contingencies
Term period of lease	60 months
Current rentable square feet of office space | ft²	7,941
Increase in rentable square feet of office space | ft²	11,471
Operating Lease Term	60 months
Base rent in first month	$ 0
Base rate in second month	15,990
Base Rent Thereafter	$ 19,412
Early lease termination for its second Ann Arbor lease | ft²		5,500

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Property and equipment, gross	$ 1,516	$ 1,279
Less accumulated depreciation and amortization	996	844
Property and equipment, net	520	435
Depreciation expense	265	258	$ 252
Lab equipment
Property and Equipment
Property and equipment, gross	232	232
Computer equipment
Property and Equipment
Property and equipment, gross	51	114
Software
Property and Equipment
Property and equipment, gross	205	206
Furniture and fixtures
Property and Equipment
Property and equipment, gross	719	568
Leasehold improvements
Property and Equipment
Property and equipment, gross	$ 309	$ 159

Other Accrued Liabilities (Deta

Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Accrued Liabilities
Accrued compensation	$ 1,833	$ 582
Accrued professional fees	1,228	153
Accrued franchise and property taxes	44	38
Accrued interest		397
Accrued other	296	48
Total other accrued liabilities	$ 3,401	$ 1,218

Investments (Details)

Investments (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash equivalents and investments
Gross Unrealized Gains					$ 1,000					$ 1,000
Gross Unrealized Losses	$ (319,000)				(846,000)				$ (319,000)	(846,000)
Total, Amortized Cost	134,138,000				270,297,000				134,138,000	270,297,000
Total, Estimated Fair Value	133,819,000				269,452,000				133,819,000	269,452,000
Amortization of premiums and discounts on investments									217,000	(334,000)	$ (1,014,000)
Other income, net	610,000	$ 651,000	$ 750,000	$ 764,000	805,000	$ 518,000	$ 323,000	$ 348,000	2,775,000	1,994,000	1,172,000
Interest Income
Cash equivalents and investments
Interest income on investments									2,600,000	2,500,000	2,600,000
Other income, net
Cash equivalents and investments
Amortization of premiums and discounts on investments									200,000	(300,000)	$ (1,000,000)
Reclassification out of accumulated other comprehensive income (loss)
Cash equivalents and investments
Other income, net									0
U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost					2,999,000					2,999,000
Investments, Estimated Fair Value					2,999,000					2,999,000
Short-term investments | U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost	44,897,000				97,537,000				44,897,000	97,537,000
Gross Unrealized Losses	(142,000)				(225,000)				(142,000)	(225,000)
Investments, Estimated Fair Value	44,755,000				97,312,000				44,755,000	97,312,000
Short-term investments | U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	50,598,000				56,143,000				50,598,000	56,143,000
Gross Unrealized Losses	(169,000)				(141,000)				(169,000)	(141,000)
Investments, Estimated Fair Value	50,429,000				56,002,000				50,429,000	56,002,000
Long-term investments | U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost					27,983,000					27,983,000
Gross Unrealized Losses					(209,000)					(209,000)
Investments, Estimated Fair Value					27,774,000					27,774,000
Long-term investments | U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost					42,041,000					42,041,000
Gross Unrealized Losses					(248,000)					(248,000)
Investments, Estimated Fair Value					41,793,000					41,793,000
Money market funds
Cash equivalents and investments
Cash equivalents, Estimated Fair Value	34,526,000				27,302,000				34,526,000	27,302,000
Certificates of deposit | Short-term investments
Cash equivalents and investments
Investments, Amortized Cost	3,873,000				12,429,000				3,873,000	12,429,000
Gross Unrealized Gains					1,000					1,000
Gross Unrealized Losses	(7,000)				(13,000)				(7,000)	(13,000)
Investments, Estimated Fair Value	3,866,000				12,417,000				3,866,000	12,417,000
Certificates of deposit | Long-term investments
Cash equivalents and investments
Investments, Amortized Cost	244,000				3,863,000				244,000	3,863,000
Gross Unrealized Losses	(1,000)				(10,000)				(1,000)	(10,000)
Investments, Estimated Fair Value	$ 243,000				$ 3,853,000				$ 243,000	$ 3,853,000

Fair Value Measurements - Recur

Fair Value Measurements - Recurring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Assets:
Available-for-sale-securities	$ 243	$ 73,420
Total, Estimated Fair Value	133,819	269,452
Transfer of assets between levels	0	0
Transfer of liabilities between levels	0	0
Recurring fair value measurement
Assets:
Money market funds	34,526	27,302
Total, Estimated Fair Value	133,819	269,452
Recurring fair value measurement | U.S. treasury notes
Assets:
Available-for-sale-securities	44,755	128,085
Recurring fair value measurement | U.S. government agency securities
Assets:
Available-for-sale-securities	50,429	97,795
Recurring fair value measurement | Certificates of deposit
Assets:
Available-for-sale-securities	4,109	16,270
Recurring fair value measurement | Level 1
Assets:
Money market funds	34,526	27,302
Total, Estimated Fair Value	83,390	171,657
Recurring fair value measurement | Level 1 | U.S. treasury notes
Assets:
Available-for-sale-securities	44,755	128,085
Recurring fair value measurement | Level 1 | Certificates of deposit
Assets:
Available-for-sale-securities	4,109	16,270
Recurring fair value measurement | Level 2
Assets:
Total, Estimated Fair Value	50,429	97,795
Recurring fair value measurement | Level 2 | U.S. government agency securities
Assets:
Available-for-sale-securities	$ 50,429	$ 97,795

Stock Compensation (Details)

Stock Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2017	Apr. 30, 2015
Stock compensation
Weighted-average period over which remaining unrecognized compensation cost will be recognized		3 years 2 months 12 days
Number of Options
Outstanding at the beginning of period (in shares)		4,159,151
Granted (in shares)		1,890,177
Forfeited or expired (in shares)		(388,796)
Exercised (in shares)		(356,809)
Outstanding at the end of the period (in shares)		5,303,723	4,159,151
Weighted-Average Exercise Price Per Share
Outstanding at the beginning of period (in dollars per share)		$ 28.13
Granted (in dollars per share)		56.63
Forfeited or expired (in dollars per share)		41.18
Exercised (in dollars per share)		32.91
Outstanding at the end of the period (in dollars per share)		$ 37.01	$ 28.13
Weighted-Average Remaining Contractual Term (Years)
Outstanding at the end of the period		7 years 5 months 1 day	7 years 4 months 21 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)		$ 83,473	$ 165,385
Information about the stock option plan
Number of Options, vested and expected to vest (in shares)		5,303,723
Number of Options, exercisable (in shares)		2,866,429
Weighted-Average Exercise Price Per Share, vested and expected to vest (in dollars per share)		$ 37.01
Weighted-Average Exercise Price Per Share, exercisable (in dollars per share)		$ 28.82
Weighted-Average Remaining Contractual Term, vested and expected to vest		7 years 5 months 1 day
Weighted-Average Remaining Contractual Term, exercisable		6 years 15 days
Aggregate Intrinsic Value, vested and expected to vest (in dollars)		$ 83,473
Aggregate Intrinsic Value, exercisable (in dollars)		65,112
Total intrinsic value of stock options exercised		12,100	$ 4,000	$ 400
Additional disclosures
Unrecognized stock-based compensation expense (in dollars)		$ 66,400
Weighted-average grant-date fair value (in dollars per share)		$ 37.56	$ 15.99	$ 9.78
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)		2.75%	2.04%	1.47%
Weighted-average expected life of options (years)		6 years 2 months 16 days	6 years 2 months 9 days	6 years 2 months 19 days
Volatility (as a percent)		72.00%	73.00%	71.00%
Stock options
Stock compensation
Stock-based compensation expense		$ 23,400	$ 18,200	$ 15,600
RSUs
Stock compensation
Stock-based compensation expense		600	$ 400	$ 400
Unrecognized stock-based compensation expense		$ 2,000
Weighted-average period over which remaining unrecognized compensation cost will be recognized		3 years 1 month 6 days
Number of Options
Granted (in shares)		37,600
Forfeited or expired (in shares)		(6,691)
Outstanding and unvested at the beginning of period (in shares)		10,003
Vested (in shares)		(3,437)
Outstanding and unvested at the ending of period (in shares)		37,475	10,003
Weighted-Average Exercise Price Per Share
Granted (in dollars per share)		$ 66.32
Forfeited or expired (in dollars per share)		54.16
Outstanding and unvested at the beginning of period (in dollars per share)		57.54
Vested (in dollars per share)		57.54
Outstanding and unvested at the at the end of the period (in dollars per share)		$ 66.96	$ 57.54
2017 Inducement Equity Plan | Maximum
Stock compensation
Shares reserved and approved for issuance					750,000
2013 Stock Option and Incentive Plan
Stock compensation
Shares reserved and approved for issuance	2,975,000					2,051,378
Increase in the number of shares of stock reserved and available for issuance	923,622
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
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

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Benefit Plan
Contributions to the 401(k) Plan	$ 0.3	$ 0.3	$ 0.2

Income Taxes - Other (Details)

Income Taxes - Other (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017
Provision for income taxes
Provision for income taxes	$ 0	$ 0	$ 0
Corporate tax rate (as a percent)	21.00%	34.00%	34.00%
Reduction in gross deferred tax assets		$ 50,400,000
Additional net income tax expense		0
Deferred tax assets
Deferred tax assets, before valuation allowance	$ 152,182,000	99,848,000	$ 75,300,000
Valuation allowance	152,182,000	99,848,000
2016-09 Accounting Standards Update
Deferred tax assets
Deferred tax assets, before valuation allowance				$ 4,500,000
Valuation allowance				$ 4,500,000
Federal
Deferred tax assets
Net operating loss carryforwards	539,200,000	347,400,000	196,400,000
State
Deferred tax assets
Net operating loss carryforwards	$ 526,600,000	$ 327,800,000	$ 18,100,000

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate
Federal income tax (benefit) at statutory rate (as a percent)	(21.00%)	(34.00%)	(34.00%)
Change in tax rate (as a percent)	(0.00%)	29.60%	0.10%
Permanent items (as a percent)	(0.50%)	0.10%	0.90%
Other (as a percent)	0.50%	(0.90%)	0.20%
Amended Tax Returns (as a percent)	(0.00%)	(4.50%)	(0.00%)
Change in valuation allowance (as a percent)	21.00%	9.70%	32.80%
Effective income tax rate (as a percent)	0.00%	0.00%	0.00%
Unrecognized tax benefits related to interest and penalties accrued	$ 0

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Federal and state operating loss carryforwards	$ 138,299	$ 88,637
Equity compensation	13,542	10,809
Temporary differences	341	402
Total deferred tax assets	152,182	99,848	$ 75,300
Valuation allowance	$ (152,182)	$ (99,848)

Net Loss Per Common Share (Deta

Net Loss Per Common Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Loss Per Common Share
Total potential dilutive shares	5,349,428	4,354,507	3,528,828
Warrants for common stock
Net Loss Per Common Share
Total potential dilutive shares	8,230	185,353	256,590
Stock options
Net Loss Per Common Share
Total potential dilutive shares	5,303,723	4,159,151	3,255,987
Unvested RSUs
Net Loss Per Common Share
Total potential dilutive shares	37,475	10,003	16,251

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 49,473	$ 41,551	$ 39,524	$ 40,940	$ 33,439	$ 40,056	$ 38,248	$ 35,860	$ 171,488	$ 147,603	$ 57,868
General and administrative	11,176	9,011	6,956	5,954	5,257	5,681	5,412	5,029	33,097	21,379	18,282
Total operating expenses	60,649	50,562	46,480	46,894	38,696	45,737	43,660	40,889	204,585	168,982	76,150
Loss from operations	(60,649)	(50,562)	(46,480)	(46,894)	(38,696)	(45,737)	(43,660)	(40,889)	(204,585)	(168,982)	(76,150)
Other income, net	610	651	750	764	805	518	323	348	2,775	1,994	1,172
Net loss	$ (60,039)	$ (49,911)	$ (45,730)	$ (46,130)	$ (37,891)	$ (45,219)	$ (43,337)	$ (40,541)	$ (201,810)	$ (166,988)	$ (74,978)
Net loss per common share (basic and diluted) (in dollars per share)	$ (2.24)	$ (1.86)	$ (1.71)	$ (1.73)	$ (1.44)	$ (1.86)	$ (1.92)	$ (1.80)	$ (7.54)	$ (6.98)	$ (3.33)
Weighted-average shares outstanding (basic and diluted) (in shares)	26,818,331	26,804,026	26,786,796	26,605,189	26,222,397	24,311,844	22,591,326	22,563,152	26,754,308	23,933,273	22,544,475

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent events - Collaboration And License Agreement With Daiichi Sankyo Europe GmbH $ in Millions	Jan. 02, 2019USD ($)
Subsequent Events
Amount of upfront cash payment to be received	$ 150
Amount of milestone cash payment to be received	$ 150
Minimum
Subsequent Events
Royalty percentage	15.00%
Maximum
Subsequent Events
Royalty percentage	25.00%