Stock Based Compensation - Stock Based Compensation Stock Option Activity (Details) - Employee Stock Option - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, Beginning Balance (in shares)	259,563
Number of Options, Granted (in shares)	0
Number of Options, Exercised (in shares)	(25,000)
Number of Options, Forfeited (in shares)	0
Number of Options, Outstanding, Ending Balance (in shares)	234,563	259,563
Number of Options, Vested and exercisable at end of period (in shares)	234,563
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding, Beginning Balance (in dollars per share)	$ 18.03
Weighted-Average Exercise Price, Granted (in dollars per share)	0.00
Weighted-Average Exercise Price, Exercised (in dollars per share)	17.22
Weighted-Average Exercise Price, Forfeited (in dollars per share)	0.00
Weighted-Average Exercise Price, Outstanding, Ending Balance (in dollars per share)	18.12	$ 18.03
Weighted Average Exercise Price, Vested and exercisable at end of period (in dollars per share)	$ 18.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 10,985
Aggregate Intrinsic Value, Exercised	1,092
Aggregate Intrinsic Value, Outstanding, Ending Balance	9,029	$ 10,985
Aggregate Intrinsic Value, Vested and exercisable at end of period	$ 9,029
Weighted-Average Remaining Contractual Life	2 years 4 months 6 days	2 years 9 months 3 days
Weighted-Average Remaining Contractual Life, Vested and exercisable at end of period	2 years 4 months 6 days