CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net income (loss)	$ (336,164)	$ (1,325,653)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	29,174	19,496
Share-based compensation	234,801	1,265,581
Other	7,268	(3,296)
Changes in assets and liabilities:
Accounts receivable	(25,667)	12,331
Prepaid expenses and other assets	(6,184)	(1,502)
Operating lease right-of-use assets	31,835	21,746
Accounts payable	7,689	8,897
Accrued expenses and other liabilities	20,391	13,133
Operating lease liabilities	(35,013)	(19,634)
Net cash used in operating activities	(71,870)	(8,901)
Investing activities
Purchases of property and equipment and intangible assets	(14,032)	(20,433)
Purchases of marketable securities	(808,180)	(527,899)
Sales of marketable securities	174,042	93,389
Maturities of marketable securities	699,133	252,164
Other investing activities	316	0
Net cash provided by (used in) investing activities	51,279	(202,779)
Financing activities
Proceeds from initial public offering, net of underwriters' discounts and commissions	0	1,573,200
Proceeds from exercise of stock options, net	64,992	744
Shares repurchased for tax withholdings on release of restricted stock units	(56,894)	(424,965)
Payment of deferred offering costs and other financing activities	(1,750)	(11,305)
Net cash provided by financing activities	6,348	1,137,674
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	(86)	(182)
Net increase (decrease) in cash, cash equivalents, and restricted cash	(14,329)	925,812
Cash, cash equivalents, and restricted cash, beginning of period	677,743	135,290
Cash, cash equivalents, and restricted cash, end of period	663,414	1,061,102
Supplemental cash flow information
Accrued property and equipment	3,952	7,174
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	$ 14,030	$ 41,399