Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue	$ 109,479	$ 81,064	$ 274,282	$ 200,414
Cost of revenue	70,166	50,147	191,633	138,955
Gross profit	39,313	30,917	82,649	61,459
Operating expenses:
Technology and development	11,483	9,781	31,245	25,739
Marketing	5,588	5,436	26,179	23,133
General and administrative	11,995	10,037	38,828	29,948
Total operating expenses	29,066	25,254	96,252	78,820
Income (loss) from operations	10,247	5,663	(13,603)	(17,361)
Interest income and other income, net:
Interest income	311	37	387	133
Other income, net	0	0	13	37
Total interest income and other income, net	311	37	400	170
Net income (loss)	10,558	5,700	(13,203)	(17,191)
Accretion of redeemable convertible preferred stock	(40,224)	(3,050)	(175,915)	56,819
Undistributed earnings attributable to participating securities	0	(2,105)	0	(31,483)
Net income (loss) attributable to common stock—basic	(29,666)	545	(189,118)	8,145
Net income (loss) attributable to common stock—diluted	$ (29,666)	$ 545	$ (189,118)	$ (17,191)
Net income (loss) per share attributable to common stock - basic (in dollars per share)	$ (0.50)	$ 0.04	$ (6.37)	$ 0.57
Net income (loss) per share attributable to common stock - diluted (in dollars per share)	$ (0.50)	$ 0.03	$ (6.37)	$ (0.25)
Weighted average shares used to compute net income (loss) per share attributable to common stock - basic	58,868,903	14,441,246	29,678,082	14,339,820
Weighted average shares used to compute net income (loss) per share attributable to common stock - diluted	58,868,903	17,855,205	29,678,082	69,761,822