Pension Plans and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Sep. 30, 2016	Dec. 31, 2006
Defined Benefit Plan Disclosure [Line Items]
Pension cost (credit)	$ 8,851	$ 9,114	$ 8,527
Health reimbursement account, amount	1,438					$ 7,310
Health reimbursement accounts funding	88	$ 133	$ 218
Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Expected amortization of gain (loss) next year	310
Supplemental Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Expected amortization of gain (loss) next year	$ 256
Qualified plan | Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Award granted, amount					$ 1,400
Qualified plan | 401(k) plan | Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Vested percentage of contributions	100.00%
Employer matching contribution as percent of employees' gross pay	3.00%
Vesting period for Company contributions	5 years
Qualified plan | Qualified defined contribution plan | Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Minimum years of service required				1 year
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%