Pension and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 1,498	$ 1,291	$ 4,494	$ 3,873
Interest cost	3,129	3,144	9,387	9,432
Expected return on plan assets	(4,031)	(3,929)	(12,093)	(11,787)
Amortization of prior service cost (credit)	64	68	192	204
Amortization of net actuarial loss	2,313	2,063	6,939	6,189
Settlement loss				1,716
Net periodic benefit cost for continuing operations	2,973	2,637	8,919	9,627
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	2,018	1,827	6,054	4,333
Interest cost	7,253	6,206	21,759	18,686
Amortization of prior service cost (credit)	261	(240)	783	(720)
Amortization of net actuarial loss	3,681	1,971	11,043	8,075
Net periodic benefit cost for continuing operations	$ 13,213	$ 9,764	$ 39,639	$ 30,374