STATEMENTS OF CAPITALIZATION (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Long-Term Debt
Unamortized discount	$ (6,686)	$ (4,033)
Total long-term debt	993,314	897,767
Long-term debt, current maturities	0	44,500
Long-term debt, noncurrent	993,314	853,267
Common Stockholder's Equity
Common stock - 200 shares authorized of $1.00 par value, 100 shares outstanding at Dec. 31, 2011 and 2010, respectively	0	0
Additional paid in capital	783,162	693,531
Retained earnings	295,201	270,257
Accumulated other comprehensive loss	(1,504)	(1,675)
Total common stockholder's equity	1,076,859	962,113
First Mortgage Bonds [Member] | Series Due Aug. 15, 2041 [Member]
Long-Term Debt
Long-term debt, gross	200,000	0
Unsecured Senior Notes [Member] | Senior E Due Oct. 1, 2016 [Member]
Long-Term Debt
Long-term debt, gross	200,000	200,000
Unsecured Senior Notes [Member] | Senior G Due Dec. 1, 2018 [Member]
Long-Term Debt
Long-term debt, gross	250,000	250,000
Unsecured Senior Notes [Member] | Senior C and D Due Oct. 1, 2033 [Member]
Long-Term Debt
Long-term debt, gross	100,000	100,000
Unsecured Senior Notes [Member] | Senior F Due Oct. 1, 2036 [Member]
Long-Term Debt
Long-term debt, gross	250,000	250,000
Pollution Control Obligations, Securing Pollution Control Revenue Bonds [Member] | Due July 1, 2011 [Member]
Long-Term Debt
Long-term debt, gross	0	44,500
Pollution Control Obligations, Securing Pollution Control Revenue Bonds [Member] | Due Sept. 1, 2016 [Member]
Long-Term Debt
Long-term debt, gross	$ 0	$ 57,300