Pension and Other Postretirement Benefits (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
Components of net periodic benefit cost:
Service cost	$ 1,498	$ 1,291	$ 2,996	$ 2,582
Interest cost	3,129	3,144	6,258	6,288
Expected return on plan assets	(4,031)	(3,929)	(8,062)	(7,858)
Amortization of prior service cost (credit)	64	68	128	136
Amortization of net actuarial loss	2,313	2,063	4,626	4,126
Settlement loss				1,716
Net periodic benefit cost for continuing operations	2,973	2,637	5,946	6,990
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	2,018	1,253	4,036	2,506
Interest cost	7,253	6,278	14,506	12,480
Amortization of prior service cost (credit)	261	(240)	522	(480)
Amortization of net actuarial loss	3,681	3,052	7,362	6,104
Net periodic benefit cost for continuing operations	$ 13,213	$ 10,343	$ 26,426	$ 20,610