CONDENSED STATEMENTS OF REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - USD ($) $ in Thousands	Common Stock Series B1 Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital Series B1 Redeemable Convertible Preferred Stock	Additional Paid-in Capital	Accumulated Deficit	Series B1 Redeemable Convertible Preferred Stock	Total
Beginning balance at Dec. 31, 2019		$ 30		$ 709,692	$ (720,890)		$ (11,168)
Beginning balance (in shares) at Dec. 31, 2019		29,672,000				24,000
Sale of common stock, net of issuance costs		$ 1		1,405			1,406
Sale of common stock, net of issuance costs (in shares)		854,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)		48,000
Issuance of common stock under employee stock purchase plan				25			25
Issuance of common stock under employee stock purchase plan (in shares)		19,000
Issuance of common stock for services rendered				26			26
Issuance of common stock for services rendered (in shares)		14,000
Stock-based compensation expense				750			750
Net income					8,817		8,817
Ending balance at Mar. 31, 2020		$ 31		711,898	(712,073)		(144)
Ending balance (in shares) at Mar. 31, 2020		30,607,000				24,000
Beginning balance at Dec. 31, 2019		$ 30		709,692	(720,890)		(11,168)
Beginning balance (in shares) at Dec. 31, 2019		29,672,000				24,000
Net income							(35,961)
Ending balance at Sep. 30, 2020		$ 35		724,381	(756,851)		(32,435)
Ending balance (in shares) at Sep. 30, 2020		35,219,000				24,000
Beginning balance at Mar. 31, 2020		$ 31		711,898	(712,073)		(144)
Beginning balance (in shares) at Mar. 31, 2020		30,607,000				24,000
Sale of common stock, net of issuance costs		$ 3		5,821			5,824
Sale of common stock, net of issuance costs (in shares)		3,607,000
Issuance of common stock under employee stock purchase plan				29			29
Issuance of common stock under employee stock purchase plan (in shares)		21,000
Issuance of common stock for services rendered				72			72
Issuance of common stock for services rendered (in shares)		56,000
Stock-based compensation expense				754			754
Net income					(24,226)		(24,226)
Ending balance at Jun. 30, 2020		$ 34		718,574	(736,299)		(17,691)
Ending balance (in shares) at Jun. 30, 2020		34,291,000				24,000
Sale of common stock and prefunded warrants, net of issuance costs		$ 1		4,936			4,937
Sale of common stock and prefunded warrants, net of issuance costs (in shares)		868,000
Issuance of common stock under employee stock purchase plan				30			30
Issuance of common stock under employee stock purchase plan (in shares)		19,000
Issuance of common stock for services rendered				72			72
Issuance of common stock for services rendered (in shares)		41,000
Stock-based compensation expense				769			769
Net income					(20,552)		(20,552)
Ending balance at Sep. 30, 2020		$ 35		724,381	(756,851)		(32,435)
Ending balance (in shares) at Sep. 30, 2020		35,219,000				24,000
Beginning balance at Dec. 31, 2020		$ 38		742,342	(833,552)		$ (91,172)
Beginning balance (in shares) at Dec. 31, 2020		38,291,000				24,000	38,291,000
Sale of common stock, net of issuance costs		$ 3		16,258			$ 16,261
Sale of common stock, net of issuance costs (in shares)		3,195,000
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				28			28
Issuance of common stock under employee stock purchase plan (in shares)		8,000
Issuance of common stock upon exercise of common stock options and warrants		$ 4		267			271
Issuance of common stock upon exercise of common stock options and warrants (in shares)		3,375,000
Issuance of common stock for services rendered				67			67
Issuance of common stock for services rendered (in shares)		16,000
Stock-based compensation expense				1,111			1,111
Conversion of preferred stock to common	$ 1		$ (1)
Conversion of preferred stock to common (in shares)	1,415,000					(14,000)
Net income					115,738		115,738
Ending balance at Mar. 31, 2021		$ 46		760,072	(717,814)		42,304
Ending balance (in shares) at Mar. 31, 2021		46,537,000				10,000
Beginning balance at Dec. 31, 2020		$ 38		742,342	(833,552)		$ (91,172)
Beginning balance (in shares) at Dec. 31, 2020		38,291,000				24,000	38,291,000
Conversion of preferred stock to common (in shares)						(23,684)
Net income							$ 102,210
Ending balance at Sep. 30, 2021		$ 53		764,300	(731,342)		$ 33,011
Ending balance (in shares) at Sep. 30, 2021		52,777,000					52,777,000
Beginning balance at Mar. 31, 2021		$ 46		760,072	(717,814)		$ 42,304
Beginning balance (in shares) at Mar. 31, 2021		46,537,000				10,000
Sale of common stock, net of issuance costs		$ 2		2,510			2,512
Sale of common stock, net of issuance costs (in shares)		2,076,000
Issuance of common stock under employee stock purchase plan				6			6
Issuance of common stock under employee stock purchase plan (in shares)		6,000
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)		2,496,000
Issuance of common stock for services rendered				63			63
Issuance of common stock for services rendered (in shares)		47,000
Stock-based compensation expense				404			404
Conversion of preferred stock to common		$ 1		(1)
Conversion of preferred stock to common (in shares)		953,000				(10,000)
Net income					(7,563)		(7,563)
Ending balance at Jun. 30, 2021		$ 52		763,051	(725,377)		37,726
Ending balance (in shares) at Jun. 30, 2021		52,115,000
Sale of common stock, net of issuance costs		$ 1		760			761
Sale of common stock, net of issuance costs (in shares)		647,000
Issuance of common stock under employee stock purchase plan				14			14
Issuance of common stock under employee stock purchase plan (in shares)		15,000
Stock-based compensation expense				475			475
Net income					(5,965)		(5,965)
Ending balance at Sep. 30, 2021		$ 53		$ 764,300	$ (731,342)		$ 33,011
Ending balance (in shares) at Sep. 30, 2021		52,777,000					52,777,000