Pension Plan and Other Postretirement Benefits - Components of net periodic pension benefit cost (Parentheticals) (Details) (Executive Survivor and Supplemental Retirement Plan, USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Amortization of Prior-Service Cost - From Other Comprehensive Income	$ 13	[1]	$ 13	[1]	$ 26	[1]	$ 26	[1]
Amortization of Net Actuarial Loss - From Other Comprehensive Income	78	[2]	43	[2]	156	[2]	86	[2]
Other nonelectric expenses
Defined Benefit Plan Disclosure [Line Items]
Amortization of Prior-Service Cost - From Other Comprehensive Income	8		8		16		16
Amortization of Net Actuarial Loss - From Other Comprehensive Income	30		7		60		14
Electric operation and maintenance expenses
Defined Benefit Plan Disclosure [Line Items]
Amortization of Prior-Service Cost - From Other Comprehensive Income	5		5		10		10
Amortization of Net Actuarial Loss - From Other Comprehensive Income	$ 48		$ 36		$ 96		$ 72

[1] Amortization of Prior Service Costs from Other Comprehensive Income Charged to: Electric Operation and Maintenance Expenses $ 5 $ 5 $ 10 $ 10 Other Nonelectric Expenses 8 8 16 16

[2] Amortization of Net Actuarial Loss from Other Comprehensive Income Charged to: Electric Operation and Maintenance Expenses $ 48 $ 36 $ 96 $ 72 Other Nonelectric Expenses 30 7 60 14