Condensed Unaudited Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Underwritten Offering	Private Placement	Preferred Stock	Common Stock	Common Stock Underwritten Offering	Common Stock Private Placement	Additional paid-in capital	Additional paid-in capital Underwritten Offering	Additional paid-in capital Private Placement	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period (in shares) at Dec. 31, 2019				0	49,627
Balance at beginning of period at Dec. 31, 2019	$ 117,203			$ 0	$ 50			$ 597,679			$ (480,526)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock compensation plan (in shares)					105
Issuance of common stock under employee stock compensation plans	179							179
Share-based compensation	2,324							2,324
Net loss	(15,076)										(15,076)
Balance at end of period (in shares) at Mar. 31, 2020				0	49,732
Balance at end of period at Mar. 31, 2020	104,630			$ 0	$ 50			600,182			(495,602)	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2019				0	49,627
Balance at beginning of period at Dec. 31, 2019	117,203			$ 0	$ 50			597,679			(480,526)
Increase (Decrease) in Stockholders' Equity
Net loss	(33,665)
Balance at end of period (in shares) at Jun. 30, 2020				0	89,489
Balance at end of period at Jun. 30, 2020	238,041			$ 0	$ 89			752,143			(514,191)	0
Balance at beginning of period (in shares) at Mar. 31, 2020				0	49,732
Balance at beginning of period at Mar. 31, 2020	104,630			$ 0	$ 50			600,182			(495,602)	0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of issuance costs (in shares)						28,503	8,649
Issuance of common stock, net of issuance costs		$ 116,883	$ 33,237			$ 28	$ 9		$ 116,855	$ 33,228
Issuance of common stock under the exercise of pre-funded warrants (in shares)					2,500
Issuance of common stock under the exercise of pre-funded warrants	0				$ 2			(2)
Issuance of common stock under employee stock compensation plan (in shares)					105
Issuance of common stock under employee stock compensation plans	7							7
Share-based compensation	1,873							1,873
Net loss	(18,589)										(18,589)
Balance at end of period (in shares) at Jun. 30, 2020				0	89,489
Balance at end of period at Jun. 30, 2020	238,041			$ 0	$ 89			752,143			(514,191)	0
Balance at beginning of period (in shares) at Dec. 31, 2020				0	90,121
Balance at beginning of period at Dec. 31, 2020	191,563			$ 0	$ 90			756,543			(565,073)	3
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock compensation plan (in shares)					49
Issuance of common stock under employee stock compensation plans	129							129
Share-based compensation	2,292							2,292
Net loss	(26,795)										(26,795)
Unrealized loss on available for sale securities, net of tax	(1)											(1)
Balance at end of period (in shares) at Mar. 31, 2021				0	90,170
Balance at end of period at Mar. 31, 2021	167,188			$ 0	$ 90			758,964			(591,868)	2
Balance at beginning of period (in shares) at Dec. 31, 2020				0	90,121
Balance at beginning of period at Dec. 31, 2020	191,563			$ 0	$ 90			756,543			(565,073)	3
Increase (Decrease) in Stockholders' Equity
Net loss	(56,938)
Balance at end of period (in shares) at Jun. 30, 2021				0	90,387
Balance at end of period at Jun. 30, 2021	139,573			$ 0	$ 90			761,491			(622,011)	3
Balance at beginning of period (in shares) at Mar. 31, 2021				0	90,170
Balance at beginning of period at Mar. 31, 2021	167,188			$ 0	$ 90			758,964			(591,868)	2
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock compensation plan (in shares)					217
Issuance of common stock under employee stock compensation plans	448							448
Share-based compensation	2,079							2,079
Net loss	(30,143)										(30,143)
Unrealized loss on available for sale securities, net of tax	1											1
Balance at end of period (in shares) at Jun. 30, 2021				0	90,387
Balance at end of period at Jun. 30, 2021	$ 139,573			$ 0	$ 90			$ 761,491			$ (622,011)	$ 3