CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance (in shares) at Dec. 31, 2018	308,373
Balance at Dec. 31, 2018	$ 1,465,399
Balance (in shares) at Mar. 31, 2019	308,373
Balance at Mar. 31, 2019	$ 1,465,399
Beginning balance (in shares) at Dec. 31, 2018		127,298
Beginning balance at Dec. 31, 2018	(594,563)	$ 1	$ 252,212	$ (1,421)	$ (845,355)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash upon exercise of stock options, net (in shares)		73
Issuance of common stock for cash upon exercise of stock options, net	110		110
Share-based compensation	694		694
Other comprehensive income (loss)	1,190			1,190
Net loss	(41,420)				(41,420)
Ending balance (in shares) at Mar. 31, 2019		127,371
Ending balance at Mar. 31, 2019	$ (633,989)	$ 1	253,016	(231)	(886,775)
Balance (in shares) at Dec. 31, 2019	0
Balance at Dec. 31, 2019	$ 0
Balance (in shares) at Mar. 31, 2020	0
Balance at Mar. 31, 2020	$ 0
Beginning balance (in shares) at Dec. 31, 2019		569,904
Beginning balance at Dec. 31, 2019	2,023,705	$ 6	4,229,778	647	(2,206,726)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Release of restricted stock units (in shares)		2,913
Release of restricted stock units	0	$ 0
Shares repurchased for tax withholdings on release of restricted stock units	$ (44,090)		(44,090)
Issuance of common stock for cash upon exercise of stock options, net (in shares)	8,923	8,923
Issuance of common stock for cash upon exercise of stock options, net	$ 20,347		20,347
Issuance of common stock related to charitable contributions (in shares)		100
Issuance of common stock related to charitable contributions	1,544		1,544
Share-based compensation	81,024		81,024
Other comprehensive income (loss)	(2,854)			(2,854)
Net loss	(141,196)				(141,196)
Ending balance (in shares) at Mar. 31, 2020		581,840
Ending balance at Mar. 31, 2020	$ 1,938,480	$ 6	$ 4,288,603	$ (2,207)	$ (2,347,922)