Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Voting Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Stockholders Equity, Ending Balance at Dec. 31, 2016	$ 103,248		$ 30	$ 685,272	$ (582,054)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2016			759,253
Issuance of common stock for exercise of stock options	166			166
Issuance of common stock for exercise of stock options, Shares			4,413
Cumulative effect of adoption of new accounting standard at Dec. 31, 2016				8	(8)
Stock-based compensation	5,905			5,905
Issuance of common stock, net of offering costs	27,422		$ 22	27,400
Issuance of common stock, net of offering costs, Shares			546,190
Net loss	(42,015)				(42,015)
Stockholders Equity, Ending Balance at Dec. 31, 2017	94,726		$ 52	718,751	(624,077)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2017			1,309,856
Issuance of common stock for exercise of stock options	180			180
Issuance of common stock for exercise of stock options, Shares			3,014
Stock-based compensation	6,796			6,796
Issuance of common stock, net of offering costs	45,996		$ 22	45,974
Issuance of common stock, net of offering costs, Shares			546,250
Issuance of common stock warrant	116			116
Net loss	(53,335)				(53,335)
Stockholders Equity, Ending Balance at Dec. 31, 2018	94,479		$ 74	771,817	(677,412)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2018			1,859,120
Issuance of common stock for exercise of stock options	445			445
Issuance of common stock for exercise of stock options, Shares			8,056
Stock-based compensation	5,695			5,695
Issuance of convertible voting preferred stock, net of offering costs	74,001	$ 1		74,000
Issuance of convertible voting preferred stock, net of offering costs, shares		103,000
Net loss	(88,275)				(88,275)
Stockholders Equity, Ending Balance at Dec. 31, 2019	$ 86,345	$ 1	$ 74	$ 851,957	$ (765,687)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2019		103,000	1,867,176