Redeemable Convertible Preferred Stock and Stockholders' Equity - Accretion of Redeemable Convertible Preferred Stock (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock	$ 0	$ (24,770)
Series A-1
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(701)
Series A-2
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(18)
Series A-3
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(1,365)
Series B
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(5,451)
Series C
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(5,008)
Series D
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(4,286)
Series E
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(1,806)
Series F
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		(3,121)
Series G
Temporary Equity [Line Items]
Accretion of redeemable convertible preferred stock		$ (3,014)