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, 2017	$ 9,905	$ 45	$ 331,609	$ (322,585)	$ 836
Balance, shares at Dec. 31, 2017		45,256,999
Net loss	(41,406)			(41,406)
Other comprehensive income	2				2
Issuance of stock, net of issue costs	40,938	$ 29	40,909
Issuance of stock, net of issue costs, shares		28,790,548
Fair value of warrants issued	355		355
Exercise of stock options	503		503
Exercise of stock options, shares		310,900
Vesting of stock units	(27)		(27)
Vesting of stock units, shares		153,601
Stock-based compensation	1,417		1,417
Balance at Jun. 30, 2018	11,687	$ 74	374,766	(363,991)	838
Balance, shares at Jun. 30, 2018		74,512,048
Balance at Mar. 31, 2018	8,198	$ 54	336,870	(329,563)	837
Balance, shares at Mar. 31, 2018		53,909,917
Net loss	(34,428)			(34,428)
Other comprehensive income	1				1
Issuance of stock, net of issue costs	36,377	$ 20	36,357
Issuance of stock, net of issue costs, shares		20,184,224
Fair value of warrants issued	87		87
Exercise of stock options	503		503
Exercise of stock options, shares		310,900
Vesting of stock units	(25)		(25)
Vesting of stock units, shares		107,007
Stock-based compensation	974		974
Balance at Jun. 30, 2018	11,687	$ 74	374,766	(363,991)	838
Balance, shares at Jun. 30, 2018		74,512,048
Balance at Dec. 31, 2018	$ 37,633	$ 95	445,192	(408,493)	839
Balance, shares at Dec. 31, 2018	95,372,236	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	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	106,297,792