Pension Plans and Other Postretirement 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
Pension Benefits
Pension plans and other postretirement benefits
Service cost		$ 511		$ 2,025
Interest cost	2,365	2,662	4,775	5,664
Expected return on plan assets	(3,189)	(3,110)	(6,377)	(5,728)
Recognized net actuarial loss	790	565	1,569	3,803
Amortization of prior service cost (credit)	53	55	106	66
Curtailment				7
Net periodic cost	19	683	73	5,837
Other Postretirement Benefits
Pension plans and other postretirement benefits
Service cost	471	336	789	531
Interest cost	289	326	640	689
Recognized net actuarial loss	48	96	236	258
Amortization of prior service cost (credit)		(5)		(12)
Net periodic cost	$ 808	$ 753	$ 1,665	$ 1,466