Benefit Plans (Schedule of Net Funded Status) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer Contributions	$ 10,000	[1]	$ 10,000	[1]	$ 20,000	[1]
Fair value of plan assets, ending balance	174,385
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected Benefit Obligation, Beginning Balance	243,640		211,183
Service cost	7,194		6,123		5,919
Interest cost	11,862		11,439		11,200
Plan amendments	0		0
Participant contributions	0		0
Actuarial gain	8,529		23,727
Benefits paid	(11,797)		(8,832)
Projected Benefit Obligation, Ending Balance	259,428		243,640		211,183
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	153,605		152,390
Actual return on plan assets	19,372		(1,352)
Participant contributions	0		0
Employer Contributions	13,205		11,399
Benefits paid	(11,797)		(8,832)
Fair value of plan assets, ending balance	174,385		153,605		152,390
Defined Benefit Plan, Funded Status of Plan [Abstract]
Funded Status	(85,043)		(90,046)
Prior service costs	1,663		1,909
Cumulative net loss	108,572		117,664
Prepaid Pension Costs	25,192		29,527
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities	(85,043)		(90,046)
Accumulated other comprehensive income	110,235		119,573
Prepaid (accrued) pension/postretirement cost	25,192		29,527
Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected Benefit Obligation, Beginning Balance	16,250		19,942
Service cost	77		54		61
Interest cost	697		886		959
Plan amendments	0		(4,794)
Participant contributions	1,199		846
Actuarial gain	(58)		1,578
Benefits paid	(3,394)		(2,262)
Projected Benefit Obligation, Ending Balance	14,771		16,250		19,942
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	0		0
Actual return on plan assets	0		0
Participant contributions	1,199		846
Employer Contributions	2,195		1,416
Benefits paid	(3,394)		(2,262)
Fair value of plan assets, ending balance	0		0		0
Defined Benefit Plan, Funded Status of Plan [Abstract]
Funded Status	(14,771)		(16,250)
Prior service costs	(4,326)		(4,794)
Cumulative net loss	4,279		4,624
Prepaid Pension Costs	(14,818)		(16,420)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities	(14,771)		(16,250)
Accumulated other comprehensive income	(47)		(170)
Prepaid (accrued) pension/postretirement cost	$ (14,818)		$ (16,420)

[1] Effective December 31, 2012, the qualified defined benefit and the supplemental non-qualified, non-funded pension plans were frozen resulting in no benefits accruing after December 31, 2012.