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	$ 5,588	$ 5,191	$ 11,175	$ 10,381
Interest cost	10,799	10,650	21,597	21,192
Expected return on plan assets	(12,195)	(12,370)	(24,390)	(24,740)
Amortization of prior service cost (credit)	68	85	137	170
Amortization of actuarial loss	4,881	3,011	9,763	5,835
Net periodic benefit cost	9,141	6,567	18,282	12,838
Pretax reclassification from AOCI included in net periodic benefit cost	4,949	3,096	9,900	6,005
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	1,167	1,198	2,333	2,395
Interest cost	1,562	1,612	3,124	3,225
Amortization of prior service cost (credit)	(168)	(168)	(337)	(337)
Amortization of actuarial loss	288	287	575	574
Net periodic benefit cost	2,849	2,929	5,695	5,857
Pretax reclassification from AOCI included in net periodic benefit cost	$ 120	$ 119	$ 238	$ 237