Stock-based Compensation and Benefits - (Summary of Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Options, beginning	1,598,318
Granted, Options	148,198
Forfeited, Options	(9,595)
Exercised, Options	(220,877,000)
Outstanding Options, ending	1,516,044	1,598,318
Options fully vested and exercisable at end of period, Options	1,152,875
Options expected to vest, Options	1,477,364
Outstanding, Weighted average exercise price, beginning	$ 20.62
Granted, Weighted average exercise price	32.74
Forfeited, Weighted average exercise price	27.69
Exercised, Weighted average exercise price	19.74
Outstanding, Weighted average exercised price, ending	21.89	$ 20.62
Options fully vested and exercisable at end of period, Weighted average exercise price	19.85
Options expected to vest, Weighted average exercise price	$ 21.64
Outstanding, Weighted average remaining contractual term in years	4 years 4 months 17 days	4 years 26 days
Options fully vested and exercisable at end of period, weighted average remaining contractual term in years	2 years 11 months 12 days
Options expected to vest, Weighted average remaining contractual term in years	4 years 2 months 27 days
Outstanding, Aggregate intrinsic value, beginning	$ 19,017
Outstanding, Outstanding, Aggregate intrinsic value, beginning	17,295	$ 19,017
Aggregate intrinsic Value of Options fully vested and exercisable at end of period	15,450
Options expected to vest, Aggregate Intrinsic Value	$ 17,220