Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock [Member] Purchase Agreement [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2016	$ 39,338	$ 30		$ 242,997	$ (203,689)
Balance (in shares) at Dec. 31, 2016		30,482,712
Stock-based compensation expense	4,790			4,790
Issuance of common stock from vesting of restricted stock, exercise of stock options and employee stock purchase plan	1,059	$ 1		1,058
Issuance of common stock from vesting of restricted stock, exercise of stock options and employee stock purchase plan (in shares)		434,938
Issuance of common stock	18,581	$ 5		18,576
Issuance of common stock (in shares)		5,031,250
Net loss	(62,428)				(62,428)
Balance at Dec. 31, 2017	1,340	$ 36		267,421	(266,117)
Balance (in shares) at Dec. 31, 2017		35,948,900
Cumulative effect of adoption of ASC 606	99				99
Stock-based compensation expense	9,897			9,897
Issuance of common stock from vesting of restricted stock, exercise of stock options and employee stock purchase plan	1,967	$ 1		1,966
Issuance of common stock from vesting of restricted stock, exercise of stock options and employee stock purchase plan (in shares)		1,211,541
Issuance of common stock	49,237	$ 7		49,230
Issuance of common stock (in shares)		7,015,000
Net loss	(51,153)				(51,153)
Balance at Dec. 31, 2018	$ 11,387	$ 44		328,514	(317,171)
Balance (in shares) at Dec. 31, 2018	44,175,441	44,175,441
Stock-based compensation expense	$ 5,458			5,458
Issuance of common stock from vesting of restricted stock, exercise of stock options and employee stock purchase plan	582	$ 1		581
Issuance of common stock from vesting of restricted stock, exercise of stock options and employee stock purchase plan (in shares)		576,245
Issuance of common stock	6,650	$ 6		6,644
Issuance of common stock (in shares)		5,486,500	413,349
Change in fair value of warrants upon modification	264			264
Issuance of warrants	660			660
Net loss	(59,006)				(59,006)
Balance at Dec. 31, 2019	$ (34,005)	$ 51		$ 342,121	$ (376,177)
Balance (in shares) at Dec. 31, 2019	50,651,535	50,651,535