Employee Benefit Plans Employee Benefit Plans 15 (Details) - SERP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Net Periodic Benefits Cost:
Service cost	$ 930	$ 799	$ 814
Interest cost	893	743	653
Amortization of prior service cost (credit)	12	25	117
Amortization of actuarial (gain) loss	777	292	431
Net periodic pension cost under accounting standards	$ 2,612	$ 1,859	$ 2,015
Weighted-average assumptions used to determine net periodic cost:
Discount rate	4.34%	4.61%	4.15%
Rate of compensation increase	4.00%	4.00%	4.00%