STATEMENTS OF REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Series B1 Redeemable Convertible Preferred Stock	Total
Beginning balance at Dec. 31, 2018	$ 27	$ 728,342	$ (664,375)		$ 63,994
Beginning balance (in shares) at Dec. 31, 2018	27,188,000
Sale of redeemable convertible preferred stock				24,000
Sale of common stock, net of issuance costs	$ 3	5,295			5,298
Sale of common stock, net of issuance costs (in shares)	2,068,000
Deemed dividend related to December 2019 Private Placement (Note 7)		(28,043)			(28,043)
Issuance of commitment shares (in shares)	270,000
Issuance of common stock under employee stock purchase plan		121			121
Issuance of common stock under employee stock purchase plan (in shares)	61,000
Issuance of common stock upon exercise of common stock options and warrants		3			3
Issuance of common stock upon exercise of common stock options and warrants (in shares)	38,000
Issuance of common stock for services rendered		129			129
Issuance of common stock for services rendered (in shares)	47,000
Stock-based compensation expense		3,845			3,845
Net income (loss)			(56,515)		(56,515)
Ending balance at Dec. 31, 2019	$ 30	709,692	(720,890)		(11,168)
Ending balance (in shares) at Dec. 31, 2019	29,672,000			24,000
Sale of common stock, net of issuance costs	$ 8	28,638			28,646
Sale of common stock, net of issuance costs (in shares)	8,218,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)	177,000
Issuance of common stock under employee stock purchase plan		113			113
Issuance of common stock under employee stock purchase plan (in shares)	76,000
Issuance of common stock upon exercise of common stock options and warrants		15			15
Issuance of common stock upon exercise of common stock options and warrants (in shares)	5,000
Issuance of common stock for services rendered		243			243
Issuance of common stock for services rendered (in shares)	143,000
Stock-based compensation expense		3,641			3,641
Net income (loss)			(112,662)		(112,662)
Ending balance at Dec. 31, 2020	$ 38	742,342	(833,552)		$ (91,172)
Ending balance (in shares) at Dec. 31, 2020	38,291,000			24,000	38,291,000
Sale of common stock, net of issuance costs	$ 6	19,509			$ 19,515
Sale of common stock, net of issuance costs (in shares)	5,918,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)	237,000
Issuance of common stock under employee stock purchase plan		59			59
Issuance of common stock under employee stock purchase plan (in shares)	49,000
Issuance of common stock upon exercise of common stock options and warrants	$ 7	264			271
Issuance of common stock upon exercise of common stock options and warrants (in shares)	5,871,000
Issuance of common stock for services rendered		152			152
Issuance of common stock for services rendered (in shares)	84,000
Stock-based compensation expense		2,537			2,537
Conversion of Series B1 preferred stock	$ 2	(2)
Conversion of Series B1 preferred stock (in shares)	2,368,000			(23,684)
Net income (loss)			98,091		98,091
Ending balance at Dec. 31, 2021	$ 53	$ 764,861	$ (735,461)		$ 29,453
Ending balance (in shares) at Dec. 31, 2021	52,818,000				52,818,000