Pension and Other Postretirement Benefits Benefit Obligation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Award vesting period	3 years
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Health care cost trend rate	8.00%	8.00%
Ultimate health care cost trend rate	5.00%	5.00%
Pension Benefits
Defined Benefit Plan Funded Status of Plan [Abstract]
Projected benefit obligation	(598,917)	(527,458)
Fair value of plan assets	430,894	389,490
Funded status	(168,023)	(137,968)
Accumulated benefit obligation	499,499	448,948
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract]
Current accrued benefit cost	(800)	(1,300)
Non-current accrued benefit cost	(167,223)	(136,668)
Net amount recognized	(168,023)	(137,968)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]
Net actuarial loss	164,064	148,118
Prior service cost (gain)	2,415	3,258
Accumulated other comprehensive loss	166,479	151,376
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net actuarial loss	15,458
Prior service cost (gain)	855
Accumulated other comprehensive loss	16,313
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.95%	4.75%
Rate of compensation increase	4.25%	4.50%
Postretirement Benefits
Defined Benefit Plan Funded Status of Plan [Abstract]
Projected benefit obligation	(83,836)	(78,999)
Fair value of plan assets	0	0
Funded status	(83,836)	(78,999)
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract]
Current accrued benefit cost	(6,800)	(7,300)
Non-current accrued benefit cost	(77,036)	(71,699)
Net amount recognized	(83,836)	(78,999)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]
Net actuarial loss	20,233	18,235
Prior service cost (gain)	(7,858)	(9,190)
Accumulated other comprehensive loss	12,375	9,045
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net actuarial loss	1,161
Prior service cost (gain)	(1,344)
Accumulated other comprehensive loss	(183)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.51%	4.25%
Rate of compensation increase	0.00%	0.00%
Health care cost trend rate	8.00%
January 1, 2019 | Postretirement Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Ultimate health care cost trend rate	5.00%