Pension Plans and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Benefits
Pension plans and other postretirement benefits
Service cost		$ 1,514
Interest cost	2,410	3,002
Expected return on plan assets	(3,188)	(2,618)
Recognized net actuarial loss	779	3,238
Amortization of prior service cost (credit)	53	11
Settlement		7
Net periodic cost	54	5,154
Other Postretirement Benefits
Pension plans and other postretirement benefits
Service cost	318	195
Interest cost	351	363
Recognized net actuarial loss	188	162
Amortization of prior service cost (credit)		(7)
Net periodic cost	$ 857	$ 713