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		15,782			15,782
Issuance of common stock upon exercise of stock options (in shares)	1,534
Issuance of common stock under employee stock purchase plan		3,062			3,062
Issuance of common stock under employee stock purchase plan (in shares)	97
Equity component of Convertible Notes, net		82,873			82,873
Issuance of common stock for public offering, net	$ 1	270,649			270,650
Issuance of common stock for public offering, net (in shares)	4,792
Vesting of restricted stock units (in shares)	853
Stock based compensation		34,406			34,406
Unrealized (loss) gain on available-for-sale securities			4,251		4,251
Cumulative-effect adjustment upon adoption				(404)	(404)
Net loss				(153,331)	(153,331)
Balance at Sep. 30, 2020	$ 9	1,383,727	5,170	(852,906)	536,000
Balance (in shares) at Sep. 30, 2020	85,281
Balance at Jun. 30, 2020	$ 8	1,093,072	5,770	(794,583)	304,267
Balance (in shares) at Jun. 30, 2020	79,717
Issuance of common stock upon exercise of stock options		4,974			4,974
Issuance of common stock upon exercise of stock options (in shares)	498
Issuance of common stock for public offering, net	$ 1	270,649			270,650
Issuance of common stock for public offering, net (in shares)	4,792
Vesting of restricted stock units (in shares)	274
Stock based compensation		15,032			15,032
Unrealized (loss) gain on available-for-sale securities			(600)		(600)
Net loss				(58,323)	(58,323)
Balance at Sep. 30, 2020	$ 9	1,383,727	5,170	(852,906)	536,000
Balance (in shares) at Sep. 30, 2020	85,281
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		10,774			$ 10,774
Issuance of common stock upon exercise of stock options (in shares)	1,051
Issuance of common stock under employee stock purchase plan		6,085			6,085
Issuance of common stock under employee stock purchase plan (in shares)	106
Issuance of common stock for public offering, net	$ 1	550,821			550,822
Issuance of common stock for public offering, net (in shares)	5,175
Issuance of common stock for IPR&D acquisition		30,901			30,901
Issuance of common stock for IPR&D acquisition (in shares)	276
Vesting of restricted stock units (in shares)	1,707
Stock based compensation		84,797			84,797
Unrealized (loss) gain on available-for-sale securities			(2,768)		(2,768)
Cumulative-effect adjustment upon adoption		(82,876)		6,198	(76,678)
Net loss				(331,152)	(331,152)
Balance at Sep. 30, 2021	$ 10	2,011,788	1,491	(1,254,272)	$ 759,017
Balance (in shares) at Sep. 30, 2021	94,538				94,538
Balance at Jun. 30, 2021	$ 9	1,399,659	2,441	(1,102,999)	$ 299,110
Balance (in shares) at Jun. 30, 2021	88,498
Issuance of common stock upon exercise of stock options		3,945			3,945
Issuance of common stock upon exercise of stock options (in shares)	268
Issuance of common stock for public offering, net	$ 1	550,821			550,822
Issuance of common stock for public offering, net (in shares)	5,176
Issuance of common stock for IPR&D acquisition		30,901			30,901
Issuance of common stock for IPR&D acquisition (in shares)	276
Vesting of restricted stock units		3			3
Vesting of restricted stock units (in shares)	320
Stock based compensation		26,459			26,459
Unrealized (loss) gain on available-for-sale securities			(950)		(950)
Net loss				(151,273)	(151,273)
Balance at Sep. 30, 2021	$ 10	$ 2,011,788	$ 1,491	$ (1,254,272)	$ 759,017
Balance (in shares) at Sep. 30, 2021	94,538				94,538