Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Private Placement	Common Stock	Common Stock Private Placement	Additional Paid-In Capital	Additional Paid-In Capital Private Placement	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2020	$ 236,492		$ 913		$ 1,628,070		$ 257	$ (1,392,748)
Balance (in shares) at Dec. 31, 2020			91,310
Conversion benefit included in Convertible Notes issued	114				114
Issuance of common stock under equity incentive plan	883		$ 1		882
Issuance of common stock under equity incentive plan (in shares)			97
Stock-based compensation expense	11,486				11,486
Net loss	(52,614)							(52,614)
Net unrealized loss on short-term investments	(136)						(136)
Comprehensive loss	(52,750)
Balance at Mar. 31, 2021	196,225		$ 914		1,640,552		121	(1,445,362)
Balance (in shares) at Mar. 31, 2021			91,407
Balance at Dec. 31, 2020	236,492		$ 913		1,628,070		257	(1,392,748)
Balance (in shares) at Dec. 31, 2020			91,310
Net loss	(166,037)
Net unrealized loss on short-term investments	(261)
Comprehensive loss	(166,298)
Balance at Sep. 30, 2021	118,843		$ 1,019		1,676,613		(4)	(1,558,785)
Balance (in shares) at Sep. 30, 2021			101,912
Balance at Mar. 31, 2021	196,225		$ 914		1,640,552		121	(1,445,362)
Balance (in shares) at Mar. 31, 2021			91,407
Conversion benefit included in Convertible Notes issued	116				116
Issuance of common stock under equity incentive plan	4,218		$ 4		4,214
Issuance of common stock under equity incentive plan (in shares)			313
Issuance of common stock under the employee stock purchase plan	1,529		$ 1		1,528
Issuance of common stock on under the employee stock purchase plan (in shares)			110
Issuance of common stock on exercise of warrants			$ 2		(2)
Issuance of common stock on exercise of warrants (in shares)			195
Issuance of common stock on conversion of notes	7,878		$ 98		7,780
Issuance of common stock on conversion of notes (in shares)			9,849
Stock-based compensation expense	11,241				11,241
Net loss	(61,015)							(61,015)
Net unrealized loss on short-term investments	(80)						(80)
Comprehensive loss	(61,095)
Balance at Jun. 30, 2021	160,112		$ 1,019		1,665,429		41	(1,506,377)
Balance (in shares) at Jun. 30, 2021			101,874
Issuance of common stock under equity incentive plan	(52)				(52)
Issuance of common stock under equity incentive plan (in shares)			38
Stock-based compensation expense	11,236				11,236
Net loss	(52,408)							(52,408)
Net unrealized loss on short-term investments	(45)						(45)
Comprehensive loss	(52,453)
Balance at Sep. 30, 2021	118,843		$ 1,019		1,676,613		(4)	(1,558,785)
Balance (in shares) at Sep. 30, 2021			101,912
Balance at Dec. 31, 2021	77,570		$ 1,020		1,689,987		(6)	(1,613,431)
Balance (in shares) at Dec. 31, 2021			102,005
Issuance of common stock under equity incentive plan	(637)		$ 1		(638)
Issuance of common stock under equity incentive plan (in shares)			138
Stock-based compensation expense	10,915				10,915
Net loss	(63,888)							(63,888)
Net unrealized loss on short-term investments	(2)						(2)
Comprehensive loss	(63,890)
Balance at Mar. 31, 2022	23,958		$ 1,021		1,700,264		(8)	(1,677,319)
Balance (in shares) at Mar. 31, 2022			102,143
Balance at Dec. 31, 2021	77,570		$ 1,020		1,689,987		(6)	(1,613,431)
Balance (in shares) at Dec. 31, 2021			102,005
Net loss	(162,155)
Net unrealized loss on short-term investments	(51)
Comprehensive loss	(162,206)
Balance at Sep. 30, 2022	22,450		$ 1,188		1,796,905		(57)	(1,775,586)
Balance (in shares) at Sep. 30, 2022			118,774
Balance at Mar. 31, 2022	23,958		$ 1,021		1,700,264		(8)	(1,677,319)
Balance (in shares) at Mar. 31, 2022			102,143
Issuance of common stock under equity incentive plan	(457)		$ 2		(459)
Issuance of common stock under equity incentive plan (in shares)			154
Issuance of common stock under the employee stock purchase plan	772		$ 2		770
Issuance of common stock on under the employee stock purchase plan (in shares)			201
Stock-based compensation expense	10,353				10,353
Net loss	(56,359)							(56,359)
Net unrealized loss on short-term investments	(3)						(3)
Comprehensive loss	(56,362)
Balance at Jun. 30, 2022	(21,736)		$ 1,025		1,710,928		(11)	(1,733,678)
Balance (in shares) at Jun. 30, 2022			102,498
Issuance of common stock in a private placement, net		$ 75,163		$ 161		$ 75,002
Issuance of common stock in a private placement, net (in shares)				16,129
Issuance of common stock under equity incentive plan	(221)		$ 2		(223)
Issuance of common stock under equity incentive plan (in shares)			147
Stock-based compensation expense	11,198				11,198
Net loss	(41,908)							(41,908)
Net unrealized loss on short-term investments	(46)						(46)
Comprehensive loss	(41,954)
Balance at Sep. 30, 2022	$ 22,450		$ 1,188		$ 1,796,905		$ (57)	$ (1,775,586)
Balance (in shares) at Sep. 30, 2022			118,774