Stock-based Compensation and Benefits - Summary of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Options, beginning	1,264,876
Granted, Options	3,749
Exercised, Options	(117,618,000)
Forfeited, Options	(40,023)
Outstanding Options, ending	1,110,984	1,264,876
Options fully vested and exercisable at end of period, Options	892,922
Options expected to vest, Options	1,093,498
Outstanding, Weighted average exercise price, beginning	$ 22.33
Granted, Weighted average exercise price	35.75
Exercised, Weighted average exercise price	20.37
Forfeited, Weighted average exercise price	30.72
Outstanding, Weighted average exercised price, ending	22.28	$ 22.33
Options fully vested and exercisable at end of period, Weighted average exercise price	20.14
Options expected to vest, Weighted average exercise price	$ 22.11
Outstanding, Weighted average remaining contractual term in years	3 years 8 months 5 days	3 years 11 months 1 day
Options fully vested and exercisable at end of period, weighted average remaining contractual term in years	2 years 6 months 11 days
Options expected to vest, Weighted average remaining contractual term in years	3 years 7 months 6 days
Outstanding, Aggregate intrinsic value, beginning	$ 11,387
Outstanding, Outstanding, Aggregate intrinsic value, beginning	12,292	$ 11,387
Aggregate intrinsic Value of Options fully vested and exercisable at end of period	11,731
Options expected to vest, Aggregate Intrinsic Value	$ 12,282