Pension Plans and Other Postretirement Employee Benefits Pension Plans and Other Postretirement Employee Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
AOCL at January 1	$ 138,747		$ 139,297		$ 140,898		$ 140,882
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Net of Tax	(1,361)	[1]	(1,405)	[1]	(2,723)	[1]	(2,678)	[1]
Amortization of actuarial loss included in net periodic cost	3,544	[1]	2,780	[1]	7,057	[1]	5,638	[1]
Other Comprehensive Income (Loss), Net of Tax	2,183	[1]	1,375	[1]	4,334	[1]	2,960	[1]
AOCL at June 30	136,564		137,922		136,564		137,922
Other Postretirement Employee Benefits [Member]
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Net of Tax	(1,480)	[1]	(1,522)	[1]	(2,961)	[1]	(2,913)	[1]
Amortization of actuarial loss included in net periodic cost	481	[1]	355	[1]	979	[1]	954	[1]
Other Comprehensive Income (Loss), Net of Tax	(999)	[1]	(1,167)	[1]	(1,982)	[1]	(1,959)	[1]
Pension Plans [Member]
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Net of Tax	119	[1]	117	[1]	238	[1]	235	[1]
Amortization of actuarial loss included in net periodic cost	3,063	[1]	2,425	[1]	6,078	[1]	4,684	[1]
Other Comprehensive Income (Loss), Net of Tax	$ 3,182	[1]	$ 2,542	[1]	$ 6,316	[1]	$ 4,919	[1]

[1] (a) Amortization of prior service cost (credit) and amortization of actuarial loss are included in the computation of net periodic cost.