Pension and Other Post-Retirement Benefits Pension Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Return on Plan Assets	$ 0
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Service Cost	2,020	1,523	1,668
Defined Benefit Plan, Interest Cost	2,570	2,134	2,175
Defined Benefit Plan, Expected Return on Plan Assets	(2,693)	(2,456)	(2,507)
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0	2	2
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	74	69	69
Defined Benefit Plan, Amortization of Gains (Losses)	1,753	687	602
Defined Benefit Plan, Net Periodic Benefit Cost	3,724	1,959	2,009
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Service Cost	548	599	567
Defined Benefit Plan, Interest Cost	538	623	574
Defined Benefit Plan, Expected Return on Plan Assets	(269)	(267)	(306)
Defined benefit plan amortization of regulatory assets	225	225	225
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	(806)	(665)	(406)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	615	613	329
Defined Benefit Plan, Amortization of Gains (Losses)	$ 851	$ 1,128	$ 983