Pension 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization of:
Total recognized in other comprehensive income (loss)	$ (1,294)	$ (1,461)	$ 37
Defined Benefit Plan
Service cost:
Benefit accrual	0	0	0
Other expenses	650	650	650
Interest cost	947	1,091	1,244
Expected return on plan assets	(1,377)	(1,493)	(1,675)
Settlement loss	0	0	0
Amortization of:
Prior service cost	0	0	0
Actuarial loss	371	389	393
Net periodic pension expense	591	637	612
Changes in plan assets and benefit obligations included in other comprehensive income (loss):
Prior service cost	0	0	0
Net actuarial loss (gain)	177	(1,619)	175
Amortization of:
Prior service cost	0	0	0
Actuarial loss	(371)	(389)	(393)
Total recognized in other comprehensive income (loss)	$ (194)	$ (2,008)	$ (218)
Weighted average assumptions used to determine expense:
Discount rate	3.50%	3.90%	4.20%
Expected return on plan assets	5.90%	6.25%	6.50%
Weighted average assumptions used to determine benefit obligations as of December 31:
Discount rate	4.20%	3.50%	3.90%
Expected return on plan assets	5.90%	6.25%	6.50%
Supplemental Defined Benefit Plans
Service cost:
Benefit accrual	$ 0	$ 0	$ 0
Other expenses	0	0	0
Interest cost	566	631	687
Expected return on plan assets	0	0	0
Settlement loss	0	0	0
Amortization of:
Prior service cost	0	0	0
Actuarial loss	310	258	233
Net periodic pension expense	876	889	920
Changes in plan assets and benefit obligations included in other comprehensive income (loss):
Prior service cost	0	0	0
Net actuarial loss (gain)	(789)	805	488
Amortization of:
Prior service cost	0	0	0
Actuarial loss	(310)	(258)	(233)
Total recognized in other comprehensive income (loss)	$ (1,099)	$ 547	$ 255
Weighted average assumptions used to determine expense:
Discount rate	3.50%	3.90%	4.20%
Weighted average assumptions used to determine benefit obligations as of December 31:
Discount rate	4.20%	3.50%	3.90%