Pension and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,645	$ 1,375	$ 3,258	$ 2,944
Interest cost	5,415	5,668	10,737	11,240
Expected return on plan assets	(8,257)	(8,130)	(16,290)	(16,030)
Amortization of prior service cost (credit)	209	287	420	562
Recognized losses	3,100	1,543	5,859	2,875
Net periodic benefit cost	2,112	743	3,984	1,591
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	59	48	136	143
Interest cost	579	685	1,259	1,424
Amortization of prior service cost (credit)	(397)	(485)	(793)	(771)
Recognized losses	256	240	542	404
Net periodic benefit cost	$ 497	$ 488	$ 1,144	$ 1,200