Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Options (in shares):
Outstanding beginning of the period (in shares)	7,532,455
Granted (in shares)	1,772,353
Forfeited (in shares)	(279,651)
Exercised (in shares)	(688,661)
Outstanding end of the period (in shares)	8,336,496		7,532,455
Exercisable at end of the period (in shares)	4,727,976
Weighted-Average Exercise Price (in dollars per share):
Outstanding beginning of the period (in dollars per share)	$ 12.22
Granted (in dollars per share)	14.99
Forfeited (in dollars per share)	14.55
Exercised (in dollars per share)	9.68
Outstanding end of the period (in dollars per share)	12.95		$ 12.22
Exercisable at the end of the period (in dollars per share)	$ 11.31
Outstanding, weighted-average remaining contractual term (years)	7 years 1 month 6 days		7 years 2 months 12 days
Exercisable, weighted-average remaining contractual term (years)	5 years 10 months 24 days
Outstanding, aggregate intrinsic value	$ 65,845		$ 19,988
Exercisable, aggregate intrinsic value	45,104
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options exercised intrinsic value	$ 5,500	$ 3,400
Options grants in period, weighted average grant date fair value (in dollars per share)	$ 6.41	$ 6.78
Options vested in period fair value	$ 7,700	$ 6,900
Options unrecognized compensation expense	$ 20,500
Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options unrecognized compensation expense, period for recognition (years)	2 years 6 months
Class A Common Stock | Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Expiration period (years)	10 years
Minimum | Class A Common Stock | Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Award vesting period (years)	3 years
Maximum | Class A Common Stock | Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Award vesting period (years)	4 years