Condensed Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Class A and Class B Common Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ (1,087,582)	$ 737,009	$ 0	$ 460	$ 8,788	$ (1,096,830)
Redeemable convertible preferred stock, Beginning balance, Shares at Dec. 31, 2019		126,046,000
Beginning balance at Dec. 31, 2019				229,750,000
Stock options exercised	692		0	$ 1	691
Stock options exercised, Shares				467,000
Stock-based compensation	2,501		0		2,501
Net (loss) income	27,346		0		0	27,346
Ending balance at Mar. 31, 2020	(1,057,043)	$ 737,009	0	$ 461	11,980	(1,069,484)
Redeemable convertible preferred stock, Ending balance, Shares at Mar. 31, 2020		126,046,000
Ending balance at Mar. 31, 2020				230,217,000
Beginning balance at Dec. 31, 2019	(1,087,582)	$ 737,009	0	$ 460	8,788	(1,096,830)
Redeemable convertible preferred stock, Beginning balance, Shares at Dec. 31, 2019		126,046,000
Beginning balance at Dec. 31, 2019				229,750,000
Stock options exercised	531
Ending balance at Jun. 30, 2020	(1,026,735)	$ 737,009	0	$ 462	14,950	(1,042,147)
Redeemable convertible preferred stock, Ending balance, Shares at Jun. 30, 2020		126,046,000
Ending balance at Jun. 30, 2020				230,439,000
Beginning balance at Dec. 31, 2019	(1,087,582)	$ 737,009	0	$ 460	8,788	(1,096,830)
Redeemable convertible preferred stock, Beginning balance, Shares at Dec. 31, 2019		126,046,000
Beginning balance at Dec. 31, 2019				229,750,000
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	737,009				736,757
Net (loss) income	4,651
Ending balance at Sep. 30, 2020	$ 756,409		$ 39		1,848,549	(1,092,179)
Redeemable convertible preferred stock, Ending balance, Shares at Sep. 30, 2020	0
Redeemable convertible preferred stock, Ending balance at Sep. 30, 2020		$ 0
Ending balance at Sep. 30, 2020			389,279,000
Beginning balance at Mar. 31, 2020	$ (1,057,043)	$ 737,009	$ 0	$ 461	11,980	(1,069,484)
Redeemable convertible preferred stock, Beginning balance, Shares at Mar. 31, 2020		126,046,000
Beginning balance at Mar. 31, 2020				230,217,000
Stock options exercised			0	$ 1	530
Stock options exercised, Shares				222,000
Stock-based compensation	2,440		0		2,440
Net (loss) income	27,337		0		0	27,337
Ending balance at Jun. 30, 2020	(1,026,735)	$ 737,009	$ 0	$ 462	14,950	(1,042,147)
Redeemable convertible preferred stock, Ending balance, Shares at Jun. 30, 2020		126,046,000
Ending balance at Jun. 30, 2020				230,439,000
Stock options exercised	4,292			$ 1	4,291
Stock options exercised, Shares			453,000	780,000
Sale of stock	100,000				100,000
Sale of stock, Shares			3,030,000
Stock-based compensation	107,825				107,825
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering		$ (737,009)		$ 252
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering, Shares		(126,046,000)		126,046,000
Issuance of Class A common stock in connection with initial public offering, net of offering costs, underwriting discounts and commissions	886,856		$ 3		886,853
Issuance of Class A common stock in connection with initial public offering, net of offering costs, underwriting discounts and commissions, Shares			28,615,000
Conversion of common stock into Class B common stock in connection with initial public offering			$ 36	$ (715)	679
Conversion of common stock into Class B common stock in connection with initial public offering, Shares			357,265,000	(357,265,000)
Vesting of restricted stock awards, Shares			1,000
Common stock withheld for tax obligations and net settlement	(2,806)				2,806
Common stock withheld for tax obligations and net settlement, Shares			(85,000)
Net (loss) income	(50,032)					(50,032)
Ending balance at Sep. 30, 2020	$ 756,409		$ 39		1,848,549	(1,092,179)
Redeemable convertible preferred stock, Ending balance, Shares at Sep. 30, 2020	0
Redeemable convertible preferred stock, Ending balance at Sep. 30, 2020		$ 0
Ending balance at Sep. 30, 2020			389,279,000
Beginning balance at Dec. 31, 2020	$ 711,359		$ 39		2,101,773	(1,390,453)
Redeemable convertible preferred stock, Beginning balance, Shares at Dec. 31, 2020		0
Redeemable convertible preferred stock, Beginning balance at Dec. 31, 2020		$ 0
Beginning balance at Dec. 31, 2020			391,660,000
Stock options exercised	2,680		$ 0		2,680
Stock options exercised, Shares			513,000
Stock-based compensation	48,254				48,254
Vesting of restricted stock units	0		$ 0		0	0
Vesting of restricted stock awards, Shares			608,000
Common stock withheld for tax obligations and net settlement	(14,902)		$ 0		(14,902)	0
Common stock withheld for tax obligations and net settlement, Shares			(324,000)
Net (loss) income	1,668					1,668
Ending balance at Mar. 31, 2021	749,059		$ 39		2,137,805	(1,388,785)
Redeemable convertible preferred stock, Ending balance, Shares at Mar. 31, 2021		0
Redeemable convertible preferred stock, Ending balance at Mar. 31, 2021		$ 0
Ending balance at Mar. 31, 2021			392,457,000
Beginning balance at Dec. 31, 2020	711,359		$ 39		2,101,773	(1,390,453)
Redeemable convertible preferred stock, Beginning balance, Shares at Dec. 31, 2020		0
Redeemable convertible preferred stock, Beginning balance at Dec. 31, 2020		$ 0
Beginning balance at Dec. 31, 2020			391,660,000
Net (loss) income	14,660
Ending balance at Sep. 30, 2021	846,396		$ 39		2,222,150	(1,375,793)
Redeemable convertible preferred stock, Ending balance, Shares at Sep. 30, 2021		0
Redeemable convertible preferred stock, Ending balance at Sep. 30, 2021		$ 0
Ending balance at Sep. 30, 2021			398,681,000
Beginning balance at Mar. 31, 2021	749,059		$ 39		2,137,805	(1,388,785)
Redeemable convertible preferred stock, Beginning balance, Shares at Mar. 31, 2021		0
Redeemable convertible preferred stock, Beginning balance at Mar. 31, 2021		$ 0
Beginning balance at Mar. 31, 2021			392,457,000
Stock options exercised	13,291				13,291
Stock options exercised, Shares			2,609,000
Stock-based compensation	42,366				42,366
Vesting of restricted stock awards, Shares			631,000
Common stock withheld for tax obligations and net settlement	(11,383)				(11,383)
Common stock withheld for tax obligations and net settlement, Shares			(304,000)
Net (loss) income	31,061					31,061
Ending balance at Jun. 30, 2021	824,394	$ 0	$ 39		2,182,079	1,357,724
Redeemable convertible preferred stock, Ending balance, Shares at Jun. 30, 2021		0
Ending balance at Jun. 30, 2021			395,393,000
Stock options exercised	14,135				14,135
Stock options exercised, Shares			2,733,000
Stock-based compensation	42,593				42,593
Vesting of restricted stock awards, Shares			985,000
Common stock withheld for tax obligations and net settlement	(16,657)				16,657
Common stock withheld for tax obligations and net settlement, Shares			(430,000)
Net (loss) income	(18,069)					(18,069)
Ending balance at Sep. 30, 2021	$ 846,396		$ 39		$ 2,222,150	$ (1,375,793)
Redeemable convertible preferred stock, Ending balance, Shares at Sep. 30, 2021		0
Redeemable convertible preferred stock, Ending balance at Sep. 30, 2021		$ 0
Ending balance at Sep. 30, 2021			398,681,000