CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Balance at Dec. 31, 2018	$ 37,633	$ 95	$ 445,192	$ (408,493)	$ 839
Balance, shares at Dec. 31, 2018		95,372,236
Net loss	(19,238)			(19,238)
Exercise of stock options	264	$ 1	263
Exercise of stock options, shares		141,760
Vesting of stock units	(20)		(20)
Vesting of stock units, shares		40,232
Stock-based compensation	1,238		1,238
Balance at Mar. 31, 2019	19,877	$ 96	446,673	(427,731)	839
Balance, shares at Mar. 31, 2019		95,554,228
Balance at Dec. 31, 2019	$ 8,330	$ 109	472,667	(465,286)	840
Balance, shares at Dec. 31, 2019	109,417,322	109,417,322
Net loss	$ (13,174)			(13,174)
Issuance of stock, net of issue costs	19,990	$ 15	19,975
Issuance of stock, net of issue costs, shares		15,000,000
Employee stock purchase plan	187	$ 1	186
Employee stock purchase plan, shares		161,660
Vesting of stock units	(19)		(19)
Vesting of stock units, shares		162,850
Stock-based compensation	1,160		1,160
Balance at Mar. 31, 2020	$ 16,474	$ 125	$ 493,969	$ (478,460)	$ 840
Balance, shares at Mar. 31, 2020	124,741,832	124,741,832