Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Cost, Changes in Plan Assets and Benefit Obligations, and AOCI Impacts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amortization of:
Total recognized in other comprehensive income (loss)	$ (1,805)	$ (1,294)	$ (1,461)
Defined Benefit Plan
Service cost:
Benefit accrual	0	0	0
Other expenses	650	650	650
Interest cost	997	947	1,091
Expected return on plan assets	(1,222)	(1,377)	(1,493)
Settlement loss	0	0	0
Amortization of:
Prior service cost	0	0	0
Actuarial loss	310	371	389
Net periodic pension expense	735	591	637
Changes in plan assets and benefit obligations included in other comprehensive income (loss):
Prior service cost	0	0	0
Net actuarial loss (gain)	(1,755)	177	(1,619)
Amortization of:
Prior service cost	0	0	0
Actuarial loss	(310)	(371)	(389)
Total recognized in other comprehensive income (loss)	$ (2,065)	$ (194)	$ (2,008)
Weighted average assumptions used to determine expense:
Discount rate	4.20%	3.50%	3.90%
Expected return on plan assets	5.75%	5.90%	6.25%
Weighted average assumptions used to determine benefit obligations as of December 31:
Discount rate	3.10%	4.20%	3.50%
Expected return on plan assets	5.75%	5.90%	6.25%
Supplemental Defined Benefit Plans
Service cost:
Benefit accrual	$ 0	$ 0	$ 0
Other expenses	0	0	0
Interest cost	620	566	631
Expected return on plan assets	0	0	0
Settlement loss	0	0	0
Amortization of:
Prior service cost	0	0	0
Actuarial loss	256	310	258
Net periodic pension expense	876	876	889
Changes in plan assets and benefit obligations included in other comprehensive income (loss):
Prior service cost	0	0	0
Net actuarial loss (gain)	516	(789)	805
Amortization of:
Prior service cost	0	0	0
Actuarial loss	(256)	(310)	(258)
Total recognized in other comprehensive income (loss)	$ 260	$ (1,099)	$ 547
Weighted average assumptions used to determine expense:
Discount rate	4.20%	3.50%	3.90%
Weighted average assumptions used to determine benefit obligations as of December 31:
Discount rate	3.10%	4.20%	3.50%