Defined Benefit Postretirement Plans (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
Defined Benefit Plan Disclosure [Line Items]
Transition obligation amortization period			20 years
Pension Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 604	$ 757	$ 1,209	$ 1,513
Interest cost	830	774	1,659	1,548
Expected return on plan assets	(1,929)	(1,675)	(3,858)	(3,350)
Net amortization	711	859	1,314	1,718
Total cost (benefit)	216	715	324	1,429
Other Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	6	5	12	10
Interest cost	75	40	150	79
Expected return on plan assets	0	0	0	0
Net amortization	(1)	(3)	222	(5)
Total cost (benefit)	$ 80	$ 42	$ 384	$ 84