Redeemable Convertible Preferred Stock and Stockholders' Equity/(Deficit) - Accretion of Redeemable Convertible Preferred Stock (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	$ (40,224)	$ (3,050)	$ (175,915)	$ 56,819
Series A-1
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(1,119)	(88)	(4,904)	1,448
Series A-2
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(28)	(2)	(123)	36
Series A-3
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(2,349)	(182)	(10,192)	3,010
Series B
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(9,284)	(1,090)	(40,336)	12,021
Series C
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(8,530)	(668)	(37,062)	11,039
Series D
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(7,300)	(571)	(31,717)	9,447
Series E
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(2,948)	(241)	(12,884)	4,102
Series F
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	(4,541)	(208)	(20,184)	7,084
Series G
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	$ (4,125)	$ 0	$ (18,513)	$ 8,632