Retirement Plans - Net Periodic Benefit Plan (Income) Cost for the Postretirement Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 0	$ 0	$ 0
Schedule Off Amounts Recognized In Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amortization of prior service cost	0	0	0
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	377	392	332
Schedule Off Amounts Recognized In Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss) before tax, beginning of period	(147)	(193)	(239)
Amortization of prior service cost	46	46	46
Accumulated other comprehensive income (loss) before tax, end of period	$ (101)	$ (147)	$ (193)