Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Balance at Dec. 31, 2019	$ 698,426	$ (1,066)	$ 12	$ 1,012,218	$ 29	$ (313,833)	$ (1,066)
Balance, Shares at Dec. 31, 2019			119,897
Vesting of early exercised stock options	32			32
Issuance of common stock pursuant to equity incentive plans	11,206		$ 1	11,205
Issuance of common stock pursuant to equity incentive plans, Shares			2,987
Issuance of common stock in connection with at-the-market offering, net of issuance costs	497,242			497,242
Issuance of common stock pursuant in connection with at-the-market offerings, net of issuance costs, Shares			4,000
Stock-based compensation expense	$ 95,348			95,348
Accounting Standards Update Extensible List	Accounting Standards Update201613 [Member]
Net income (loss)	$ (84,813)					(84,813)
Balance at Sep. 30, 2020	1,216,375		$ 13	1,616,045	29	(399,712)
Balance, Shares at Sep. 30, 2020			126,884
Balance at Jun. 30, 2020	1,015,553		$ 12	1,428,171	29	(412,659)
Balance, Shares at Jun. 30, 2020			124,584
Vesting of early exercised stock options	6			6
Issuance of common stock pursuant to equity incentive plans	5,329		$ 1	5,328
Issuance of common stock pursuant to equity incentive plans, Shares			1,304
Issuance of common stock in connection with at-the-market offering, net of issuance costs	147,633			147,633
Issuance of common stock pursuant in connection with at-the-market offerings, net of issuance costs, Shares			996
Stock-based compensation expense	34,907			34,907
Net income (loss)	12,947					12,947
Balance at Sep. 30, 2020	1,216,375		$ 13	1,616,045	29	(399,712)
Balance, Shares at Sep. 30, 2020			126,884
Balance at Dec. 31, 2020	1,328,015		$ 13	1,660,379	29	(332,406)
Balance, Shares at Dec. 31, 2020			128,004
Vesting of early exercised stock options	4			4
Issuance of common stock pursuant to equity incentive plans	13,433			13,433
Issuance of common stock pursuant to equity incentive plans, Shares			3,515
Issuance of common stock in connection with at-the-market offering, net of issuance costs	989,615			989,615
Issuance of common stock pursuant in connection with at-the-market offerings, net of issuance costs, Shares			2,637
Stock-based compensation expense	133,866			133,866
Net income (loss)	218,698					218,698
Balance at Sep. 30, 2021	2,683,631		$ 13	2,797,297	29	(113,708)
Balance, Shares at Sep. 30, 2021			134,156
Balance at Jun. 30, 2021	2,561,028		$ 13	2,743,629	29	(182,643)
Balance, Shares at Jun. 30, 2021			133,299
Issuance of common stock pursuant to equity incentive plans	3,148			3,148
Issuance of common stock pursuant to equity incentive plans, Shares			857
Stock-based compensation expense	50,520			50,520
Net income (loss)	68,935					68,935
Balance at Sep. 30, 2021	$ 2,683,631		$ 13	$ 2,797,297	$ 29	$ (113,708)
Balance, Shares at Sep. 30, 2021			134,156