Condensed Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss)/Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		62,965,000
Beginning balance at Dec. 31, 2018	$ 201,167	$ 6	$ 522,503	$ (799)	$ (320,543)
Stock-based compensation expense	1,762		1,762
Common stock issued upon exercise of stock options (in shares)		119,000
Common stock issued upon exercise of stock options	162		162
Common stock issued upon release of restricted stock units (in shares)		397,000
Restricted stock surrendered for taxes (in shares)		(145,000)
Restricted stock surrendered for taxes	0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(504)		(504)
Foreign currency translation adjustments	42			42
Unrealized gain (loss) on marketable securities, net	3			3
Net loss	(14,489)				(14,489)
Ending balance (in shares) at Mar. 31, 2019		63,336,000
Ending balance at Mar. 31, 2019	188,143	$ 6	523,923	(754)	(335,032)
Beginning balance (in shares) at Dec. 31, 2019		67,329,000
Beginning balance at Dec. 31, 2019	174,957	$ 7	560,704	(725)	(385,029)
Stock-based compensation expense	$ 3,409		3,409
Issuance of common stock, net of issuance costs of $332 (in shares)	10,925,000
Issuance of common stock, net of issuance costs of $332	$ 140,873	$ 1	140,872
Common stock issued upon exercise of stock options (in shares)	1,310,000	1,310,000
Common stock issued upon exercise of stock options	$ 9,650		9,650
Common stock issued upon exercise of warrants (in shares)	7,000
Common stock issued upon release of restricted stock units (in shares)		462,000
Restricted stock surrendered for taxes (in shares)		(155,000)
Restricted stock surrendered for taxes	$ (1,922)		(1,922)
Foreign currency translation adjustments	(54)			(54)
Unrealized gain (loss) on marketable securities, net	(54)			(54)
Net loss	(22,906)				(22,906)
Ending balance (in shares) at Mar. 31, 2020		79,878,000
Ending balance at Mar. 31, 2020	$ 303,953	$ 8	$ 712,713	$ (833)	$ (407,935)