Retirement Plans Retirement Plans - Net Periodic Pension Cost - SERP (Details) - SERP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ (268)	$ (287)	$ (323)
Net amortization and other	(223)	(211)	(343)
Total net periodic pension earnings/(cost)	$ (491)	$ (498)	$ (666)