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	(30,736)			(30,736)
Other comprehensive income	1				1
Issuance of stock, net of issue costs	18,343	$ 10	18,333
Issuance of stock, net of issue costs, shares		10,526,500
Exercise of stock options	308	$ 1	307
Exercise of stock options, shares		166,760
Vesting of stock units	(73)		(73)
Vesting of stock units, shares		232,296
Stock-based compensation	2,734		2,734
Balance at Jun. 30, 2019	28,210	$ 106	466,493	(439,229)	840
Balance, shares at Jun. 30, 2019		106,297,792
Balance at Mar. 31, 2019	19,877	$ 96	446,673	(427,731)	839
Balance, shares at Mar. 31, 2019		95,554,228
Net loss	(11,498)			(11,498)
Other comprehensive income	1				1
Issuance of stock, net of issue costs	18,343	$ 10	18,333
Issuance of stock, net of issue costs, shares		10,526,500
Exercise of stock options	44		44
Exercise of stock options, shares		25,000
Vesting of stock units	(53)		(53)
Vesting of stock units, shares		192,064
Stock-based compensation	1,496		1,496
Balance at Jun. 30, 2019	28,210	$ 106	466,493	(439,229)	840
Balance, shares at Jun. 30, 2019		106,297,792
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	$ (26,124)			(26,124)
Employee stock purchase plan	187	$ 1	186
Employee stock purchase plan, shares		161,660
Issuance of stock, net of issue costs	19,990	$ 15	19,975
Issuance of stock, net of issue costs, shares		15,000,000
Vesting of stock units	(90)		(90)
Vesting of stock units, shares		618,917
Stock-based compensation	1,895		1,895
Balance at Jun. 30, 2020	$ 4,188	$ 125	494,633	(491,410)	840
Balance, shares at Jun. 30, 2020	125,197,899	125,197,899
Balance at Mar. 31, 2020	$ 16,474	$ 125	493,969	(478,460)	840
Balance, shares at Mar. 31, 2020		124,741,832
Net loss	(12,950)			(12,950)
Vesting of stock units	(71)		(71)
Vesting of stock units, shares		456,067
Stock-based compensation	735		735
Balance at Jun. 30, 2020	$ 4,188	$ 125	$ 494,633	$ (491,410)	$ 840
Balance, shares at Jun. 30, 2020	125,197,899	125,197,899