Retirement Plans Retirement Plans - Net Periodic Pension Cost - SERP (Details) - SERP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ (303)	$ (268)	$ (287)
Net amortization and other	(62)	(223)	(211)
Total net periodic pension earnings/(cost)	$ (365)	$ (491)	$ (498)