Retirement Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Pension plan
Earnings (cost) components:
Interest cost	$ (170)	$ (194)
Expected return on plan assets	322	262
Net amortization and deferral	(34)	(38)
Total net periodic pension earnings	118	30
SERP
Earnings (cost) components:
Interest cost	(114)	(152)
Net amortization and deferral	(44)	(32)
Total net periodic pension earnings	$ (158)	$ (184)