Defined Benefit Postretirement Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Transition obligation amortization period (in years)	20		20
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 757	$ 668	$ 2,270	$ 2,003
Interest cost	774	874	2,322	2,621
Expected return on plan assets	(1,676)	(1,914)	(5,026)	(5,742)
Net amortization	992	408	2,710	1,221
Total cost (benefit)	847	36	2,276	103
Other Benefits [Member]
Components of net periodic benefit cost:
Service cost	6	5	16	15
Interest cost	40	57	119	171
Expected return on plan assets	0	0	0	0
Net amortization	(3)	9	(8)	27
Total cost (benefit)	$ 43	$ 71	$ 127	$ 213