Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	$ 3,833	$ 3,187
Interest cost	25,144	24,064
Expected return on plan assets	(32,094)	(31,053)
Amortization of prior service credit	(1,748)	(1,750)
Amortization of actuarial loss	17,755	12,671
Net periodic benefit cost	12,890	7,119
Other Post-retirement Benefits [Member]
Components of Net Periodic Benefit Cost
Interest cost	67	117
Amortization of prior service credit	(233)	(265)
Amortization of actuarial loss	317	433
Net periodic benefit cost	$ 151	$ 285