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	$ 10	$ 445,277	$ (408,493)	$ 839
Balance, shares at Dec. 31, 2018		9,537,151
Net loss	(56,793)			(56,793)
Other comprehensive income	1				1
Issuance of stock, net of issue costs	22,627	$ 1	22,626
Issuance of stock, net of issue costs, shares		1,352,538
Exercise of stock options	414		414
Exercise of stock options, shares		22,342
Vesting of stock units	(120)		(120)
Vesting of stock units, shares		29,628
Stock-based compensation	4,568		4,568
Balance at Dec. 31, 2019	$ 8,330	$ 11	472,765	(465,286)	840
Balance, shares at Dec. 31, 2019	10,941,659	10,941,659
Net loss	$ (45,394)			(45,394)
Other comprehensive income	1				1
Issuance of stock, net of issue costs	49,853	$ 7	49,846
Issuance of stock, net of issue costs, shares		7,100,815
Employee stock purchase plan	294		294
Employee stock purchase plan, shares		33,697
Vesting of stock units	(90)		(90)
Vesting of stock units, shares		63,810
Stock-based compensation	5,547		5,547
Balance at Dec. 31, 2020	$ 18,541	$ 18	$ 528,362	$ (510,680)	$ 841
Balance, shares at Dec. 31, 2020	18,139,981	18,139,981