Pension and Other Post-Retirement Benefits Amounts Recognized as Regulatory Asset (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized as Regulatory Asset [Line Items]
Amounts Recognized as Regulatory Asset - Transition Obligation	$ 0	$ 0
Amounts Recognized as Regulatory Asset - Prior Service Cost	(2,766)	(3,563)
Amounts Recognized as Regulatory Asset - Net Loss	4,590	6,234
Total Recognized as a Regulatory Asset	1,824	2,671
Pension Plans, Defined Benefit [Member]
Amounts Recognized as Regulatory Asset [Line Items]
Amounts Recognized as Regulatory Asset - Transition Obligation	0	0
Amounts Recognized as Regulatory Asset - Prior Service Cost	249	309
Amounts Recognized as Regulatory Asset - Net Loss	18,069	13,553
Total Recognized as a Regulatory Asset	$ 18,318	$ 13,862