Consolidation and Nature of Operations (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Operating Revenues
Other revenues	$ 1,130	$ 3,379	$ 2,003	$ 4,216
Operating Expenses
Operations and maintenance	210,590	213,609	465,619	419,922
Depreciation and amortization	106,617	102,995	213,200	203,629
Taxes other than income taxes	40,155	31,682	77,779	63,405
Other expenses	1,396	1,325	3,216	2,403
Other
Other income	557	943	2,247	1,892
Other expense (Note 11)	(3,186)	(5,650)	(4,927)	(7,176)
Interest Expense
Interest charges	60,140	60,751	121,217	121,518
Allowance for borrowed funds used during construction	(3,856)	(3,072)	(7,432)	(6,091)
Income Taxes	50,818	51,188	44,813	43,535
Income From Continuing Operations	93,185	93,314	82,817	105,005
Income From Discontinued Operations	654	26,252	1,348	13,664
Balance Sheets
Current Assets - Regulatory assets	56,158		56,158		62,286
Current Assets - Deferred income taxes	113,243		113,243		124,897
Current Assets - Assets held for sale	30,540		30,540		2,861
Current Assets - Other current assets	30,103		30,103		25,501
Deferred Debits - Regulatory assets	983,394		983,394		986,370
Current Liabilities - Deferred fuel and purchased power regulatory liability	54,359		54,359		58,442
Current Liabilities - Other regulatory liabilities	88,557		88,557		80,526
Deferred Credits and Other - Deferred income taxes	1,825,077		1,825,077		1,863,861
Deferred Credits and Other - Regulatory liabilities	695,036		695,036		614,063
Cash Flows from Operating Activities
Other current assets			(37,053)	(8,340)
Other current liabilities			3,967	(26,583)
Change in other long-term assets			(26,185)	(11,015)
Change in other long-term liabilities			57,748	(48,045)
Reclassifications for discontinued operations
Operating Revenues
Other revenues		(17,799)		(25,892)
Operating Expenses
Operations and maintenance		(1,495)		(3,024)
Depreciation and amortization		(22)		(41)
Taxes other than income taxes		(2)		(3)
Other expenses		(14,391)		(20,241)
Other
Other income		10		73
Other expense (Note 11)		10		(42)
Interest Expense
Interest charges		10		72
Allowance for borrowed funds used during construction		32		60
Income Taxes		(641)		(1,122)
Income From Continuing Operations		(1,270)		(1,562)
Income From Discontinued Operations		1,270		1,562
Reclassifications for regulatory assets and liabilities and to conform to current year presentation
Balance Sheets
Current Assets - Regulatory assets					62,286
Current Assets - Deferred income taxes					30,295
Current Assets - Assets held for sale					2,861
Current Assets - Other current assets					(2,861)
Deferred Debits - Regulatory assets					(62,286)
Current Liabilities - Deferred fuel and purchased power regulatory liability					58,442
Current Liabilities - Other regulatory liabilities					80,526
Deferred Credits and Other - Deferred income taxes					30,295
Deferred Credits and Other - Deferred fuel and purchased power regulatory liability					(58,442)
Deferred Credits and Other - Regulatory liabilities					(80,526)
Cash Flows from Operating Activities
Other current assets				5,456
Other current liabilities				(3,864)
Change in other long-term assets				(5,473)
Change in other long-term liabilities				3,881
As previously reported
Operating Revenues
Other revenues		21,178		30,108
Operating Expenses
Operations and maintenance		215,104		422,946
Depreciation and amortization		103,017		203,670
Taxes other than income taxes		31,684		63,408
Other expenses		15,716		22,644
Other
Other income		933		1,819
Other expense (Note 11)		(5,660)		(7,134)
Interest Expense
Interest charges		60,741		121,446
Allowance for borrowed funds used during construction		(3,104)		(6,151)
Income Taxes		51,829		44,657
Income From Continuing Operations		94,584		106,567
Income From Discontinued Operations		24,982		12,102
Balance Sheets
Current Assets - Deferred income taxes					94,602
Current Assets - Other current assets					28,362
Deferred Debits - Regulatory assets					1,048,656
Deferred Credits and Other - Deferred income taxes					1,833,566
Deferred Credits and Other - Deferred fuel and purchased power regulatory liability					58,442
Deferred Credits and Other - Regulatory liabilities					694,589
Cash Flows from Operating Activities
Other current assets				(13,796)
Other current liabilities				(22,719)
Change in other long-term assets				(5,542)
Change in other long-term liabilities				(51,926)
Amount reported after reclassification
Operating Revenues
Other revenues		3,379		4,216
Operating Expenses
Operations and maintenance		213,609		419,922
Depreciation and amortization		102,995		203,629
Taxes other than income taxes		31,682		63,405
Other expenses		1,325		2,403
Other
Other income		943		1,892
Other expense (Note 11)		(5,650)		(7,176)
Interest Expense
Interest charges		60,751		121,518
Allowance for borrowed funds used during construction		(3,072)		(6,091)
Income Taxes		51,188		43,535
Income From Continuing Operations		93,314		105,005
Income From Discontinued Operations		26,252		13,664
Balance Sheets
Current Assets - Regulatory assets					62,286
Current Assets - Deferred income taxes					124,897
Current Assets - Assets held for sale					2,861
Current Assets - Other current assets					25,501
Deferred Debits - Regulatory assets					986,370
Current Liabilities - Deferred fuel and purchased power regulatory liability					58,442
Current Liabilities - Other regulatory liabilities					80,526
Deferred Credits and Other - Deferred income taxes					1,863,861
Deferred Credits and Other - Regulatory liabilities					614,063
Cash Flows from Operating Activities
Other current assets				(8,340)
Other current liabilities				(26,583)
Change in other long-term assets				(11,015)
Change in other long-term liabilities				$ (48,045)