Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Number of Option Shares
Options outstanding (in shares) | shares	6,551,314
Granted (in shares) | shares	663,343
Exercised (in shares) | shares	(1,302,501)
Forfeited (in shares) | shares	(42,945)
Options outstanding (in shares) | shares	5,869,211
Options outstanding, weighted average remaining contractual term	3 years 11 months 19 days
Options outstanding, aggregate intrinsic value | $	$ 28,470
Weighted-Average Exercise Price
Options outstanding (in dollars per share) | $ / shares	$ 12.29
Granted (in dollars per share) | $ / shares	30.75
Exercised (in dollars per share) | $ / shares	8.70
Forfeited (in dollars per share) | $ / shares	16.67
Options outstanding (in dollars per share) | $ / shares	$ 15.14
Options Exercisable
Options exercisable (in shares) | shares	3,099,460
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 12.83
Options exercisable, weighted average remaining contractual term	3 years 3 months
Options exercisable, aggregate intrinsic value | $	$ 17,992