Redeemable Convertible Preferred Stock and Stockholders' Equity/(Deficit) - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 $ / shares shares	Aug. 02, 2017	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Temporary Equity And Stockholder's Equity [Abstract]
Conversion basis			1
Redeemable convertible preferred stock, authorized (in shares)	166,266,114	0
Redeemable convertible preferred stock, issued (in shares)	55,422,002	0
Redeemable convertible preferred stock outstanding (in shares)	55,422,002	0		55,422,002	55,422,002
Temporary Equity [Line Items]
Underwritten public offering proceeds trigger | $	$ 50,000
Percentage of outstanding shareholders to request redemption	0.67
Common stock, authorized (in shares)	290,081,638	500,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Preferred stock, authorized (in shares)	0	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Preferred stock, outstanding (in shares)	0	0
Series A-1
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	4,378,284
Redeemable convertible preferred stock, issued (in shares)	1,459,427
Redeemable convertible preferred stock outstanding (in shares)	1,459,427
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 0.3426
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.0273
Series A-2
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	109,552
Redeemable convertible preferred stock, issued (in shares)	36,517
Redeemable convertible preferred stock outstanding (in shares)	36,517
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 0.2913
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.0234
Series A-3
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	9,099,610
Redeemable convertible preferred stock, issued (in shares)	3,033,202
Redeemable convertible preferred stock outstanding (in shares)	3,033,202
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 0.0855
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.0069
Series B
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	36,338,577
Redeemable convertible preferred stock, issued (in shares)	12,112,853
Redeemable convertible preferred stock outstanding (in shares)	12,112,853
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 0.6603
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.0528
Series C
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	33,388,982
Redeemable convertible preferred stock, issued (in shares)	11,129,656
Redeemable convertible preferred stock outstanding (in shares)	11,129,656
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 1.0782
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.0864
Series D
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	28,574,005
Redeemable convertible preferred stock, issued (in shares)	9,524,665
Redeemable convertible preferred stock outstanding (in shares)	9,524,665
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 1.0782
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.0864
Series E
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	12,041,148
Redeemable convertible preferred stock, issued (in shares)	4,013,712
Redeemable convertible preferred stock outstanding (in shares)	4,013,712
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 3.7182
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.2976
Series F
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	20,808,580
Redeemable convertible preferred stock, issued (in shares)	6,936,186
Redeemable convertible preferred stock outstanding (in shares)	6,936,186
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 7.2858
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.5829
Series G
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	21,527,376
Redeemable convertible preferred stock, issued (in shares)	7,175,784
Redeemable convertible preferred stock outstanding (in shares)	7,175,784
Temporary Equity [Line Items]
Original issue price | $ / shares	$ 9.8931
Temporary equity, dividend rate (in dollars per share) | $ / shares	$ 0.7914