Pension and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Net periodic cost for pension and other postretirement benefits
Service cost	$ 897	$ 1,039
Interest cost	6,618	7,344
Expected return on plan assets	(8,311)	(8,524)
Plan net loss (gain)	2,658	1,596
Prior service cost (gain)	197	283
Transition obligation (asset)	(3)	(5)
Net curtailment/settlement loss (gain)
Net periodic benefit cost	2,056	1,733
Other Postretirement Benefits [Member]
Net periodic cost for pension and other postretirement benefits
Service cost	2
Interest cost	160	203
Expected return on plan assets
Plan net loss (gain)	35	58
Prior service cost (gain)	193	(63)
Transition obligation (asset)	5	192
Net curtailment/settlement loss (gain)
Net periodic benefit cost	$ 395	$ 390