Pension Plans and Other Postretirement Employee Benefits Pension Plans and Other Postretirement Employee Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
AOCL at January 1	$ 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	1,362	[1]	1,273
Amortization of actuarial loss included in net periodic cost	3,513	[1]	2,858
Other Comprehensive Income (Loss), Net of Tax	2,151	[1]	1,585
AOCL at March 31	138,747		139,297
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	1,481	[1]	1,390
Amortization of actuarial loss included in net periodic cost	497	[1]	599
Other Comprehensive Income (Loss), Net of Tax	(984)	[1]	(791)
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)
Amortization of actuarial loss included in net periodic cost	3,016	[1]	2,259
Other Comprehensive Income (Loss), Net of Tax	$ 3,135	[1]	$ 2,376

[1] (a)