Equity-based Compensation - Additional Stock Option Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount collected from stock option exercises	$ 822	$ 306	$ 2,748
Total intrinsic value of stock option exercises	370	47	1,108
Tax benefit of stock option exercises recorded in income tax expense	63	0	0
Tax benefit of stock option exercises recorded in additional paid-in-capital	0	315	209
Aggregate intrinsic value of outstanding stock options	386	102	173
Aggregate intrinsic value of exercisable stock options	$ 386	$ 102	$ 169
Share price (in dollars per share)	$ 25.43	$ 23.70	$ 19.31