Long-Term Debt and Financing Obligations (Details) (USD $)						0 Months Ended		1 Months Ended																																							0 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Nuclear Fuel Financing	Dec. 31, 2011 Working Capital and General Purpose	Dec. 31, 2011 Revolving Credit Facility	Nov. 14, 2011 Revolving Credit Facility Expiring September 2014	Nov. 15, 2011 Revolving Credit Facility Expiring September 2016	Jun. 29, 2008 Short Term Borrowing	Dec. 31, 2011 Bonds and Notes		Dec. 31, 2010 Bonds and Notes		Dec. 31, 2011 Pollution Control Bonds		Dec. 31, 2010 Pollution Control Bonds		Dec. 31, 2011 Pollution Control Bonds 7.25% 2009 Series A Refunding Bonds, due 2040		Dec. 31, 2010 Pollution Control Bonds 7.25% 2009 Series A Refunding Bonds, due 2040		Dec. 31, 2011 Pollution Control Bonds 4.80% 2005 Series A Refunding Bonds, due 2040		Dec. 31, 2010 Pollution Control Bonds 4.80% 2005 Series A Refunding Bonds, due 2040		Dec. 31, 2011 Pollution Control Bonds 7.25% 2009 Series B Refunding Bonds, due 2040		Dec. 31, 2010 Pollution Control Bonds 7.25% 2009 Series B Refunding Bonds, due 2040		Dec. 31, 2011 Pollution Control Bonds 4.00% 2002 Series A Refunding Bonds, due 2032		Dec. 31, 2010 Pollution Control Bonds 4.00% 2002 Series A Refunding Bonds, due 2032		Dec. 31, 2011 Senior Notes		Dec. 31, 2010 Senior Notes		Dec. 31, 2011 Senior Notes 6.00% Senior Notes, Net of Discount, due 2035		Dec. 31, 2010 Senior Notes 6.00% Senior Notes, Net of Discount, due 2035		May 01, 2005 Senior Notes 6.00% Senior Notes, Net of Discount, due 2035	Dec. 31, 2011 Senior Notes 7.50% Senior Notes, Net of Discount, due 2038		Dec. 31, 2010 Senior Notes 7.50% Senior Notes, Net of Discount, due 2038		Jun. 01, 2008 Senior Notes 7.50% Senior Notes, Net of Discount, due 2038	Aug. 31, 2010 RGRT Senior Notes	Dec. 31, 2011 RGRT Senior Notes		Dec. 31, 2010 RGRT Senior Notes		Aug. 18, 2010 RGRT Senior Notes	Dec. 31, 2011 RGRT Senior Notes 3.67% Senior Notes, Series A, due 2015		Dec. 31, 2010 RGRT Senior Notes 3.67% Senior Notes, Series A, due 2015		Dec. 31, 2011 RGRT Senior Notes 4.47% Senior Notes, Series B, due 2017		Dec. 31, 2010 RGRT Senior Notes 4.47% Senior Notes, Series B, due 2017		Dec. 31, 2011 RGRT Senior Notes 5.04% Senior Notes, Series C, due 2020		Dec. 31, 2010 RGRT Senior Notes 5.04% Senior Notes, Series C, due 2020		Dec. 31, 2011 Financing Obligations Revolving Credit Facility		Dec. 31, 2010 Financing Obligations Revolving Credit Facility
Debt Instrument [Line Items]
Long-term Debt	$ 883,176,000	$ 854,449,000							$ 849,797,000	[1]	$ 849,745,000	[1]	$ 193,135,000	[2]	$ 193,135,000	[2]	$ 63,500,000	[2]	$ 63,500,000	[2]	$ 59,235,000	[2]	$ 59,235,000	[2]	$ 37,100,000	[2]	$ 37,100,000	[2]	$ 33,300,000	[2]	$ 33,300,000	[2]	$ 546,662,000	[3]	$ 546,610,000	[3]	$ 397,894,000	[3]	$ 397,856,000	[3]		$ 148,768,000	[3]	$ 148,754,000	[3]			$ 110,000,000	[1]	$ 110,000,000	[1]		$ 15,000,000	[1]	$ 15,000,000	[1]	$ 50,000,000	[1]	$ 50,000,000	[1]	$ 45,000,000	[1]	$ 45,000,000	[1]
Long-term Line of Credit					33,379,000																																																												33,379,000	[4]	4,704,000	[4]
Long-term Debt, Current Maturities	(33,300,000)	0
Line of Credit, Current	(33,379,000)	(4,704,000)
Long-term debt	816,497,000	849,745,000
Number of tax exempt bond series													4
Debt Instrument, Interest Rate, Effective Percentage																	7.46%		7.46%		5.32%		5.32%		7.49%		7.49%		5.07%		5.07%						7.12%		7.12%			7.67%		7.67%									3.87%		3.87%		4.62%		4.62%		5.16%		5.16%
Debt Instrument, Interest Rate, Stated Percentage													4.00%				7.25%		7.25%		4.80%		4.80%		7.25%		7.25%		4.00%		4.00%						6.00%		6.00%		6.00%	7.50%		7.50%		7.50%							3.67%		3.67%		4.47%		4.47%		5.04%		5.04%
Debt Instrument, Face Amount																																									400,000,000					150,000,000						110,000,000
Debt Instrument, Unamortized Discount																																									2,300,000	1,300,000
Repayments of Short-term Debt								44,000,000
Redemption Price of Notes Equal to Principal Amount, Percentage																																																				100.00%
Proceeds from Issuance of Long-term Debt																																															109,400,000
Line of Credit Facility, Current Borrowing Capacity						200,000,000	200,000,000
Line of Credit Facility, Maximum Borrowing Capacity							300,000,000
Line of Credit Facility Term						4 years
Line of Credit Facility, Amount Outstanding			$ 13,400,000	$ 20,000,000
Line of Credit Weighted Average Interest Rate					1.50%

[1] RGRT Senior NotesOn August 17, 2010, the Company and RGRT, a Texas grantor trust through which the Company finances its portion of fuel for Palo Verde, entered into a Note Purchase Agreement (the “Agreement”) with various institutional purchasers. Under the terms of the Agreement, RGRT sold to the purchasers $110 million aggregate principal amount of senior notes (the "Notes"). The Company guarantees the payment of principal and interest on the Notes. In the Company’s financial statements, the assets and liabilities of the RGRT are reported as assets and liabilities of the Company.RGRT will pay interest on the Notes on February 15 and August 15 of each year until maturity. RGRT may redeem the Notes, in whole or in part, at any time at a redemption price equal to 100% of the principal amount to be redeemed together with the interest on such principal amount accrued to the date of redemption, plus a make-whole amount based on the prevailing market interest rates. The Agreement requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2011.The sale of the Notes was made by RGRT in reliance on a private placement exemption from registration under the Securities Act of 1933, as amended.The proceeds of $109.4 million, net of issuance costs, from the sale of the Notes was used by RGRT to repay amounts borrowed under the revolving credit facility and will enable future nuclear fuel financing requirements of RGRT to be met with a combination of the Notes and amounts borrowed from the revolving credit facility.

[2] Pollution Control Bonds (“PCBs”)The Company has four series of tax exempt unsecured PCBs in aggregate principal amount of $193.1 million. The 4.00% 2002 Series A must be remarketed in August 2012 and is shown as current maturities of long-term debt on the Company's 2011 balance sheet.

[3] Senior NotesThe Senior Notes are unsecured obligations of the Company. They were issued pursuant to bond covenants that provide limitations on the Company’s ability to enter into certain transactions. The 6.00% senior notes have an aggregate principal amount of $400.0 million and were issued in May 2005. The proceeds, net of a $2.3 million discount, were used to fund the retirement of the Company's first mortgage bonds. The Company amortizes the loss associated with a cash flow hedge recorded in accumulated other comprehensive income to earnings as interest expense over the life of the 6.00% senior notes. See Note O, "Financial Instruments and Investments - Treasury Rate Locks". This amortization is included in the effective interest rate of the 6.00% senior notes. The 7.50% senior notes have an aggregate principal amount of $150.0 million and were issued in June 2008. The proceeds, net of a $1.3 million discount, were used to repay short-term borrowings of $44.0 million, fund capital expenditures and for other general corporate purposes.

[4] Revolving Credit FacilityPrior to November 15, 2011, the Company had available a $200 million credit facility with a four-year term ending September 2014. The credit facility provided for the financing of nuclear fuel, which was accomplished through the RGRT that borrowed under the facility to acquire and process nuclear fuel. The Company was obligated to repay the RGRT’s borrowings with interest. Any amounts not borrowed by the RGRT could have been borrowed by the Company for working capital needs.On November 15, 2011, the Company and RGRT entered into an amended and restated revolving credit agreement (the “RCF”) with JP Morgan Chase Bank, N.A., as administrative agent and issuing bank, and Union Bank, N.A., as syndication agent, and various lending banks party thereto. Under the terms of the RCF, the Company and RGRT have available $200 million of credit for a term ending September 23, 2016. The Company may request that the RCF be increased up to a total of $300 million during the term of the RCF, subject to lender approval.The RCF provides that amounts borrowed by the Company may be used for, among other things, working capital and general corporate purposes. Any amounts borrowed by RGRT may be used, among other things, to finance the acquisition and processing of nuclear fuel. Amounts borrowed by RGRT are guaranteed by the Company and the balance borrowed under the RCF is recorded as short-term borrowings on the consolidated balance sheet. The RCF is unsecured. The RCF requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2011. As of December 31, 2011, the total amount borrowed by RGRT was $13.4 million for nuclear fuel under the RCF, and $20.0 million was outstanding under this facility for working capital and general corporate purposes. The weighted average interest rate on the RCF was 1.5% as of December 31, 2011.