Redeemable Convertible Preferred Stock and Stockholders' Deficit - Accretion of Redeemable Convertible Preferred Stock (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	$ (110,921)	$ 65,082	$ (135,690)	$ 59,869	$ (55,502)
Series A-1
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(3,085)	1,620	(3,785)	1,535
Series A-2
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(77)	41	(95)	38
Series A-3
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(6,478)	3,275	(7,843)	3,192
Series B
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(25,601)	13,443	(31,052)	13,111
Series C
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(23,523)	12,352	(28,531)	11,707
Series D
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(20,131)	10,571	(24,417)	10,019
Series E
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(8,130)	4,695	(9,936)	4,342
Series F
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(12,522)	8,322	(15,643)	7,292
Series G
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	$ (11,374)	$ 10,763	$ (14,388)	$ 8,633