Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Summary of Significant Accounting Policies [Abstract]
Pension and post-retirement benefits	$ 21,341	$ 17,829
Unrecovered Income Taxes - Regulatory Asset	9,871	7,355
Deferred Revenue	3,644	3,883
Other Regulatory Assets	3,151	2,464
Regulatory Assets	38,007	31,531
Other Regulated Liabilities, Current	499	0
Unamortized Investment Tax Credits	1,490	1,313
Deferred Future Income Taxes and Other	11,215	7,355
Regulatory Liabilities	$ 13,204	$ 8,668