Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Common Stock Class A and B Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2018		219,176
Beginning balance at Dec. 31, 2018		$ 5,152,047
Ending balance (in shares) at Mar. 31, 2019		219,176
Ending balance at Mar. 31, 2019		$ 5,152,047
Beginning balance (in shares) at Dec. 31, 2018			22,438
Beginning balance at Dec. 31, 2018	$ (2,871,281)		$ 0		$ 73,916	$ (2,945,330)	$ 133
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			7,121
Issuance of common stock upon exercise of stock options	1,599				1,599
Issuance of common stock upon settlement of restricted stock units (in shares)			17,688
Shares withheld related to net share settlement (in shares)			(11,415)
Shares withheld related to net share settlement	(785,004)				(785,004)
Vesting of early exercised stock options	2				2
Stock-based compensation	859,486				859,486
Other comprehensive income (loss)	2,053						2,053
Net loss	(1,138,473)					(1,138,473)
Ending balance (in shares) at Mar. 31, 2019			35,832
Ending balance at Mar. 31, 2019	(3,931,618)		$ 0		149,999	(4,083,803)	2,186
Beginning balance (in shares) at Dec. 31, 2018		219,176
Beginning balance at Dec. 31, 2018		$ 5,152,047
Ending balance (in shares) at Sep. 30, 2019		0
Ending balance at Sep. 30, 2019		$ 0
Beginning balance (in shares) at Dec. 31, 2018			22,438
Beginning balance at Dec. 31, 2018	(2,871,281)		$ 0		73,916	(2,945,330)	133
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	4,496
Net loss	(2,246,189)
Ending balance (in shares) at Sep. 30, 2019			297,584
Ending balance at Sep. 30, 2019	2,989,514		$ 3		8,176,401	(5,191,519)	4,629
Beginning balance (in shares) at Mar. 31, 2019		219,176
Beginning balance at Mar. 31, 2019		$ 5,152,047
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)		(219,176)
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering		$ (5,152,047)
Ending balance (in shares) at Jun. 30, 2019		0
Ending balance at Jun. 30, 2019		$ 0
Beginning balance (in shares) at Mar. 31, 2019			35,832
Beginning balance at Mar. 31, 2019	(3,931,618)		$ 0		149,999	(4,083,803)	2,186
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			250
Issuance of common stock upon exercise of stock options	940				940
Issuance of common stock upon settlement of restricted stock units (in shares)			3,476
Shares withheld related to net share settlement (in shares)			(1,478)
Shares withheld related to net share settlement	(80,076)				(80,076)
Issuance of common stock in connection with initial public offering, net of offering costs, underwriting discounts and commissions (in shares)			35,497
Issuance of common stock in connection with initial public offering, net of offering costs, underwriting discounts and commissions	2,483,623		$ 1		2,483,622
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)			219,176
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	5,152,047		$ 2		5,152,045
Cancelled escrow shares related to a business combination (in shares)			(2)
Cancelled escrow shares related to a business combination	(90)				(90)
Stock-based compensation	293,238				293,238
Other comprehensive income (loss)	3,307						3,307
Net loss	(644,239)					(644,239)
Ending balance (in shares) at Jun. 30, 2019			292,751
Ending balance at Jun. 30, 2019	3,277,132		$ 3		7,999,678	(4,728,042)	5,493
Ending balance (in shares) at Sep. 30, 2019		0
Ending balance at Sep. 30, 2019		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			2,562
Issuance of common stock upon exercise of stock options	12,449				12,449
Issuance of common stock upon settlement of restricted stock units (in shares)			3,772
Shares withheld related to net share settlement (in shares)			(1,501)
Shares withheld related to net share settlement	(77,902)				(77,902)
Stock-based compensation	242,176				242,176
Other comprehensive income (loss)	(864)						(864)
Net loss	(463,477)					(463,477)
Ending balance (in shares) at Sep. 30, 2019			297,584
Ending balance at Sep. 30, 2019	2,989,514		$ 3		8,176,401	(5,191,519)	4,629
Beginning balance (in shares) at Dec. 31, 2019		0
Beginning balance at Dec. 31, 2019		$ 0
Ending balance (in shares) at Mar. 31, 2020		0
Ending balance at Mar. 31, 2020		$ 0
Beginning balance (in shares) at Dec. 31, 2019				302,596
Beginning balance at Dec. 31, 2019	2,854,084			$ 3	8,398,927	(5,547,571)	2,725
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				504
Issuance of common stock upon exercise of stock options	2,329				2,329
Issuance of common stock upon settlement of restricted stock units (in shares)				3,838
Shares withheld related to net share settlement (in shares)				(146)
Shares withheld related to net share settlement	(6,763)				(6,763)
Stock-based compensation	159,978				159,978
Other comprehensive income (loss)	(4,066)						(4,066)
Net loss	(398,073)					(398,073)
Ending balance (in shares) at Mar. 31, 2020				306,792
Ending balance at Mar. 31, 2020	2,607,489			$ 3	8,554,471	(5,945,644)	(1,341)
Beginning balance (in shares) at Dec. 31, 2019		0
Beginning balance at Dec. 31, 2019		$ 0
Ending balance (in shares) at Sep. 30, 2020		0
Ending balance at Sep. 30, 2020		$ 0
Beginning balance (in shares) at Dec. 31, 2019				302,596
Beginning balance at Dec. 31, 2019	2,854,084			$ 3	8,398,927	(5,547,571)	2,725
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	4,615
Net loss	(1,294,702)
Ending balance (in shares) at Sep. 30, 2020				317,490
Ending balance at Sep. 30, 2020	2,003,093			$ 3	8,838,023	(6,842,273)	7,340
Beginning balance (in shares) at Mar. 31, 2020		0
Beginning balance at Mar. 31, 2020		$ 0
Ending balance (in shares) at Jun. 30, 2020		0
Ending balance at Jun. 30, 2020		$ 0
Beginning balance (in shares) at Mar. 31, 2020				306,792
Beginning balance at Mar. 31, 2020	2,607,489			$ 3	8,554,471	(5,945,644)	(1,341)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				153
Issuance of common stock upon exercise of stock options	757				757
Issuance of common stock upon settlement of restricted stock units (in shares)				4,813
Issuance of common stock under employee stock purchase plan (in shares)				463
Issuance of common stock under employee stock purchase plan	11,071				11,071
Shares withheld related to net share settlement (in shares)				(145)
Shares withheld related to net share settlement	(4,437)				(4,437)
Equity component of the convertible senior notes issued, net of tax and offering costs	139,224				139,224
Purchase of capped calls	(132,681)				(132,681)
Stock-based compensation	105,803				105,803
Other comprehensive income (loss)	6,445						6,445
Net loss	(437,112)					(437,112)
Ending balance (in shares) at Jun. 30, 2020				312,076
Ending balance at Jun. 30, 2020	2,296,559			$ 3	8,674,208	(6,382,756)	5,104
Ending balance (in shares) at Sep. 30, 2020		0
Ending balance at Sep. 30, 2020		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)				97
Issuance of common stock upon exercise of stock options	413				413
Issuance of common stock upon settlement of restricted stock units (in shares)				5,435
Shares withheld related to net share settlement (in shares)				(118)
Shares withheld related to net share settlement	(3,315)				(3,315)
Stock-based compensation	166,717				166,717
Other comprehensive income (loss)	2,236						2,236
Net loss	(459,517)					(459,517)
Ending balance (in shares) at Sep. 30, 2020				317,490
Ending balance at Sep. 30, 2020	$ 2,003,093			$ 3	$ 8,838,023	$ (6,842,273)	$ 7,340