Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Benefit Plan
Periodic costs for employee retirement benefit plans
Service Cost	$ 575	$ 550
Interest Cost	617	604
Expected Return on Assets	(724)	(615)
Amortization of Unrecognized Losses	408	387
Amortization of Unrecognized Prior Service Cost (Credit)	2	2
Amortization of Transition Obligation
Net Periodic Benefit Cost	878	928
Other Benefits Plan
Periodic costs for employee retirement benefit plans
Service Cost	334	446
Interest Cost	399	467
Expected Return on Assets	(406)	(314)
Amortization of Unrecognized Losses	516	441
Amortization of Unrecognized Prior Service Cost (Credit)	(432)
Amortization of Transition Obligation		34
Net Periodic Benefit Cost	$ 411	$ 1,074