Borrowings and Other Financing Instruments, Intercompany Borrowing Arrangement and Other Short-Term Borrowings (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Notes payable to affiliates	$ 550	$ 550
Intercompany Borrowing Arrangement [Member]
Short-term Debt [Line Items]
Notes payable to affiliates	$ 550	$ 550
Weighted average interest rate at end of period (in hundredths)	0.33%	0.33%