Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	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 gain (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, 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 gain (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