Stock-based Compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Number Of Options
Outstanding at December 31, 2017 (in shares)	13,180,950
Options granted (in shares)	0
Options exercised (in shares)	(2,653,008)
Options forfeited (in shares)	(367,541)
Options canceled (in shares)	(9,879)
Outstanding at September 30, 2018 (in shares)	10,150,522	13,180,950
Options exercisable at September 30, 2018 (in shares)	7,750,226
Weighted- Average Exercise Price
Outstanding at December 31, 2017 (in dollars per share)	$ 6.30
Options granted (in dollars per share)	0.00
Options exercised (in dollars per share)	5.17
Options forfeited (in dollars per share)	9.45
Options canceled (in dollars per share)	8.26
Outstanding at September 30, 2018 (in dollars per share)	6.48	$ 6.30
Options exercisable at September 30, 2018 (in dollars per share)	$ 5.67
Stock Option Activity, Additional Disclosures
Weighted average remaining contractual life outstanding	6 years 3 months 8 days	7 years 7 days
Weighted average remaining contractual life exercisable	5 years 9 months 15 days
Options outstanding, Aggregate intrinsic value	$ 124,054	$ 329,786
Options exercisable, Aggregate intrinsic value	$ 100,976