Components of Net Periodic Benefit Cost (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 [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 559	$ 1,218	$ 1,119	$ 2,436
Interest cost	846	917	1,692	1,833
Expected return on plan assets	(827)	(815)	(1,655)	(1,629)
Amortization of transition obligation	0	0	0	0
Net amortization of prior service cost	(4)	41	(8)	83
Net amortization of net (gain) loss	523	567	1,046	1,135
Net Periodic Benefit Cost	1,097	1,928	2,194	3,858
Post-Retirement Health Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	17	15	34	30
Interest cost	43	43	87	86
Expected return on plan assets	0	0	0	0
Amortization of transition obligation	15	15	30	30
Net amortization of prior service cost	0	0	0	0
Net amortization of net (gain) loss	0	0	0	0
Net Periodic Benefit Cost	$ 75	$ 73	$ 151	$ 146