Retirement Plans - Net Periodic Pension Cost - Pension Plan (Details) - Pension plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cost components:
Service cost	$ 0	$ (15)	$ (223)
Interest cost	(365)	(386)	(406)
Expected return on plan assets	585	531	517
Net amortization and deferral	(64)	(122)	(184)
Settlement recognition	0	47	0
Total net periodic pension earnings/(cost)	$ 156	$ 55	$ (296)