CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts	$ 2,703	$ 1,577
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	76,141,345	76,141,345
Redeemable convertible preferred stock, shares issued	61,279,079	61,279,079
Redeemable convertible preferred stock, shares outstanding	61,279,079	61,279,079
Redeemable convertible preferred stock, liquidation preference	$ 120,047	$ 120,047
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	36,945,317	33,740,323
Common stock, shares outstanding	36,945,317	33,740,323