Benefit Plans Benefit Plans - Future Benefit Payments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2012	$ 23,112
2013	24,647
2014	27,716
2015	28,674
2016	30,631
2017-2021	185,451
Other Benefits before Medicare Part D
Defined Benefit Plan Disclosure [Line Items]
2012	1,940
2013	1,917
2014	1,893
2015	1,836
2016	1,785
2017-2021	7,785
Other Benefits after Medicare Part D Subsidy
Defined Benefit Plan Disclosure [Line Items]
2012	1,735
2013	1,715
2014	1,694
2015	1,641
2016	1,596
2017-2021	$ 6,981