Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance at Dec. 31, 2019	$ 8	$ 976,955	$ 919	$ (699,171)	$ 278,711
Balance (in shares) at Dec. 31, 2019	78,005
Issuance of common stock upon exercise of stock options		3,826			3,826
Issuance of common stock upon exercise of stock options (in shares)	356
Vesting of restricted stock units (in shares)	291
Stock based compensation		7,418			7,418
Unrealized (loss) gain on available-for-sale securities			4,747		4,747
Cumulative-effect adjustment upon adoption				(403)	(403)
Net loss				(35,372)	(35,372)
Balance at Mar. 31, 2020	$ 8	988,199	5,666	(734,946)	258,927
Balance (in shares) at Mar. 31, 2020	78,652
Balance at Dec. 31, 2020	$ 9	1,411,286	4,259	(929,318)	$ 486,236
Balance (in shares) at Dec. 31, 2020	86,223				86,223
Issuance of common stock upon exercise of stock options		4,570			$ 4,570
Issuance of common stock upon exercise of stock options (in shares)	575
Vesting of restricted stock units (in shares)	632
Stock based compensation		23,232			23,232
Unrealized (loss) gain on available-for-sale securities			(1,062)		(1,062)
Cumulative-effect adjustment upon adoption		(82,876)		6,198	(76,678)
Net loss				(63,853)	(63,853)
Balance at Mar. 31, 2021	$ 9	$ 1,356,212	$ 3,197	$ (986,973)	$ 372,445
Balance (in shares) at Mar. 31, 2021	87,430				87,430