Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	$ 3,818	$ 3,195	$ 7,651	$ 6,382
Interest cost	25,125	24,077	50,269	48,141
Expected return on plan assets	(32,068)	(31,073)	(64,162)	(62,126)
Amortization of prior service credit	(1,744)	(1,753)	(3,492)	(3,503)
Amortization of actuarial loss	17,740	12,678	35,495	25,349
Net periodic benefit cost	12,871	7,124	25,761	14,243
Other Post-retirement Benefits [Member]
Components of Net Periodic Benefit Cost
Interest cost	67	116	134	233
Amortization of prior service credit	(233)	(265)	(466)	(530)
Amortization of actuarial loss	317	434	634	867
Net periodic benefit cost	$ 151	$ 285	$ 302	$ 570