CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		77,456,180
Beginning balance (in shares)		77,464,781
Beginning balance at Dec. 31, 2018	$ 44,207	$ 77	$ 230,154	$ (186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(6,480)			(6,480)
Share-based compensation	326		326
Sales of common stock under 2014 ESPP (in shares)		8,601
Sales of common stock under 2014 ESPP	7		7
Ending balance (in shares) at Mar. 31, 2019		77,464,781
Ending balance at Mar. 31, 2019	38,060	$ 77	230,487	(192,504)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		101,265,896
Beginning balance at Dec. 31, 2018	44,207	$ 77	230,154	(186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(60,815)
Ending balance (in shares) at Jun. 30, 2019		101,265,896
Ending balance at Jun. 30, 2019	15,369	$ 101	262,107	(246,839)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		77,464,781
Beginning balance (in shares)		101,265,896
Beginning balance at Mar. 31, 2019	38,060	$ 77	230,487	(192,504)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(54,335)			(54,335)
Share-based compensation	356		356
Exercise of stock options (in shares)		30,000
Exercise of stock options	45		45
Exercise of common stock warrants (in shares)		3,361,115
Exercise of common stock warrants	3,434	$ 4	3,430
Issuance of common stock under ATM offering, net of issuance costs (in shares)		20,410,000
Issuance of common stock under ATM offering, net of issuance costs	27,809	$ 20	27,789
Ending balance (in shares) at Jun. 30, 2019		101,265,896
Ending balance at Jun. 30, 2019	15,369	$ 101	262,107	(246,839)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		101,265,896
Beginning balance (in shares)		106,801,409
Beginning balance (in shares)		109,991,553
Beginning balance at Dec. 31, 2019	(26,700)	$ 107	266,717	(293,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	41,564			41,564
Share-based compensation	407		407
Sales of common stock under 2014 ESPP (in shares)		2,785
Sales of common stock under 2014 ESPP	1		1
Issuance of common stock under ATM offering, net of issuance costs (in shares)		3,187,359
Issuance of common stock under ATM offering, net of issuance costs	3,179	$ 3	3,176
Ending balance (in shares) at Mar. 31, 2020		109,991,553
Ending balance at Mar. 31, 2020	18,451	$ 110	270,301	(251,960)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		116,627,653
Beginning balance at Dec. 31, 2019	(26,700)	$ 107	266,717	(293,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 15,220
Exercise of stock options (in shares)	0
Exercise of common stock warrants (in shares)	0
Ending balance (in shares) at Jun. 30, 2020		116,627,653
Ending balance at Jun. 30, 2020	$ (2,628)	$ 116	275,560	(278,304)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		109,991,553
Beginning balance (in shares)		116,627,653
Beginning balance at Mar. 31, 2020	18,451	$ 110	270,301	(251,960)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(26,344)			(26,344)
Share-based compensation	491		491
Issuance of common stock under ATM offering, net of issuance costs (in shares)		6,636,100
Issuance of common stock under ATM offering, net of issuance costs	4,774	$ 6	4,768
Ending balance (in shares) at Jun. 30, 2020		116,627,653
Ending balance at Jun. 30, 2020	$ (2,628)	$ 116	$ 275,560	$ (278,304)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		116,627,653