Pension and Other Post-Retirement Benefit Plans (Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 4,996	$ 0
Change in benefit obligation [Roll Forward]
Obligation, beginning balance	690,729	740,783
Service cost	0	0	$ 0
Interest cost	31,299	29,135	33,585
Plan transfers	3,313	1,603
Defined Benefit Plan, Benefit Obligation, Benefits Paid	31,718	29,439
Actuarial (gain) loss	85,408	(51,353)
Obligation, ending balance	779,031	690,729	740,783
Defined benefit plan, plan assets, return of excess premiums	0	963
Change in plan assets [Roll Forward]
Plan assets, beginning balance	625,646	681,573
Actual gain on plan assets	144,108	(51,274)
Employer contributions	5,414	22,220
Plan assets, ending balance	746,763	625,646	681,573
Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	0	0
Change in benefit obligation [Roll Forward]
Obligation, beginning balance	3,824	4,056
Service cost	107	123	158
Interest cost	148	127	142
Plan transfers	0	0
Defined Benefit Plan, Benefit Obligation, Benefits Paid	365	365
Actuarial (gain) loss	(7)	(117)
Obligation, ending balance	3,707	3,824	4,056
Defined benefit plan, plan assets, return of excess premiums	0	0
Change in plan assets [Roll Forward]
Plan assets, beginning balance	0	0
Actual gain on plan assets	0	0
Employer contributions	365	365
Plan assets, ending balance	0	0	$ 0
Other Current Liabilities [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(3,796)	(3,971)
Other Current Liabilities [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(431)	(451)
Other Noncurrent Liabilities [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(33,468)	(61,112)
Other Noncurrent Liabilities [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (3,276)	$ (3,373)