Pension and Other Post-Retirement Benefit Plans (Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plans [Member]
Change in benefit obligation [Roll Forward]
Obligation, beginning balance	$ 777,320	$ 807,992
Service cost	0	0	$ 0
Interest cost	35,872	34,584	39,517
Plan transfers	1,226	2,558
Benefits paid	(33,593)	(32,696)
Defined Benefit Plan, Settlements, Benefit Obligation	0	0	(98,700)
Actuarial (gain) loss	10,357	(35,118)
Obligation, ending balance	791,182	777,320	807,992
Change in plan assets [Roll Forward]
Plan assets, beginning balance	672,153	719,787
Actual gain on plan assets	69,836	(23,677)
Employer contributions	6,263	6,181
Plan assets, ending balance	715,885	672,153	719,787
Post-Retirement Healthcare Plans [Member]
Change in benefit obligation [Roll Forward]
Obligation, beginning balance	4,999	6,163
Service cost	123	177	239
Interest cost	170	192	286
Plan transfers	0	0
Benefits paid	(667)	(788)
Defined Benefit Plan, Settlements, Benefit Obligation	560	0
Actuarial (gain) loss	166	(745)
Obligation, ending balance	4,231	4,999	6,163
Change in plan assets [Roll Forward]
Plan assets, beginning balance	0	0
Actual gain on plan assets	0	0
Employer contributions	667	788
Plan assets, ending balance	0	0	$ 0
Other Current Liabilities [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan	(1,357)	(1,346)
Other Current Liabilities [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan	(458)	(626)
Other Noncurrent Liabilities [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan	(73,940)	(103,821)
Other Noncurrent Liabilities [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan	$ (3,773)	$ (4,373)