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	26			26
Issuance of common stock pursuant to equity incentive plans	5,877			5,877
Issuance of common stock pursuant to equity incentive plans, Shares			1,683
Issuance of common stock in connection with at-the-market offering, net of issuance costs	349,609			349,609
Issuance of common stock pursuant in connection with at-the-market offerings, net of issuance costs, Shares			3,004
Stock-based compensation expense	$ 60,441			60,441
Accounting Standards Update Extensible List	us-gaap:AccountingStandardsUpdate201613Member
Net income (loss)	$ (97,760)					(97,760)
Balance at Jun. 30, 2020	1,015,553		$ 12	1,428,171	29	(412,659)
Balance, Shares at Jun. 30, 2020			124,584
Balance at Mar. 31, 2020	675,913		$ 12	1,045,383	29	(369,511)
Balance, Shares at Mar. 31, 2020			120,657
Vesting of early exercised stock options	9			9
Issuance of common stock pursuant to equity incentive plans	3,134			3,134
Issuance of common stock pursuant to equity incentive plans, Shares			923
Issuance of common stock in connection with at-the-market offering, net of issuance costs	349,609			349,609
Issuance of common stock pursuant in connection with at-the-market offerings, net of issuance costs, Shares			3,004
Stock-based compensation expense	30,036			30,036
Net income (loss)	(43,148)					(43,148)
Balance at Jun. 30, 2020	1,015,553		$ 12	1,428,171	29	(412,659)
Balance, Shares at Jun. 30, 2020			124,584
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	10,285			10,285
Issuance of common stock pursuant to equity incentive plans, Shares			2,658
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	83,346			83,346
Net income (loss)	149,763					149,763
Balance at Jun. 30, 2021	2,561,028		$ 13	2,743,629	29	(182,643)
Balance, Shares at Jun. 30, 2021			133,299
Balance at Mar. 31, 2021	2,441,312		$ 13	2,697,380	29	(256,110)
Balance, Shares at Mar. 31, 2021			132,304
Issuance of common stock pursuant to equity incentive plans	3,580			3,580
Issuance of common stock pursuant to equity incentive plans, Shares			995
Stock-based compensation expense	42,669			42,669
Net income (loss)	73,467					73,467
Balance at Jun. 30, 2021	$ 2,561,028		$ 13	$ 2,743,629	$ 29	$ (182,643)
Balance, Shares at Jun. 30, 2021			133,299