CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating revenue:
Electric	$ 461,657	$ 470,511	$ 1,076,291	$ 1,082,038
Gas	180,728	207,823	565,493	643,789
Other	101	283	520	1,302
Total operating revenue	642,486	678,617	1,642,304	1,727,129
Energy costs:
Purchased electricity	112,543	156,098	287,587	355,213
Electric generation fuel	40,737	19,861	99,823	89,798
Residential exchange	(14,963)	(15,302)	(37,515)	(38,637)
Purchased gas	79,487	96,462	269,470	329,981
Unrealized (gain) loss on derivative instruments, net	27,376	(64,076)	(48,316)	(59,350)
Utility operations and maintenance	130,286	128,195	259,521	256,241
Non-utility expense and other	(959)	(74)	(1,953)	787
Depreciation	90,301	84,552	178,480	163,558
Amortization	6,433	11,547	12,177	24,890
Conservation amortization	22,469	28,518	56,576	62,921
Taxes other than income taxes	53,695	72,960	153,638	172,830
Total operating expenses	547,405	518,741	1,229,488	1,358,232
Operating income	95,081	159,876	412,816	368,897
Other income (deductions):
Other income	10,844	18,337	22,857	33,273
Other expense	(1,454)	(1,947)	(2,996)	(5,700)
Non-hedged interest rate derivative expense	1,232	(7,297)	2,260	(6,770)
Interest charges:
AFUDC	3,162	4,687	7,810	11,982
Interest expense	(108,917)	(95,964)	(204,733)	(203,165)
Income (loss) before income taxes	(52)	77,692	238,014	198,517
Income tax (benefit) expense	(957)	20,000	69,634	52,346
Net income (loss)	905	57,692	168,380	146,171
Subsidiaries [Member]
Operating revenue:
Electric	461,657	470,511	1,076,291	1,082,038
Gas	180,728	207,823	565,493	643,789
Other	101	283	409	1,302
Total operating revenue	642,486	678,617	1,642,193	1,727,129
Energy costs:
Purchased electricity	112,543	156,098	287,587	355,213
Electric generation fuel	40,737	19,861	99,823	89,798
Residential exchange	(14,963)	(15,302)	(37,515)	(38,637)
Purchased gas	79,487	96,462	269,470	329,981
Unrealized (gain) loss on derivative instruments, net	27,376	(59,850)	(45,365)	(49,715)
Utility operations and maintenance	130,286	128,195	259,521	256,241
Non-utility expense and other	3,028	2,270	6,120	5,500
Depreciation	90,301	84,552	178,480	163,558
Amortization	6,433	11,547	12,177	24,890
Conservation amortization	22,469	28,518	56,576	62,921
Taxes other than income taxes	53,695	72,960	153,638	172,830
Total operating expenses	551,392	525,311	1,240,512	1,372,580
Operating income	91,094	153,306	401,681	354,549
Other income (deductions):
Other income	10,846	18,329	22,857	33,262
Other expense	(1,454)	(1,947)	(2,996)	(5,700)
Interest charges:
AFUDC	3,162	4,687	7,810	11,982
Interest expense	(65,773)	(62,333)	(131,749)	(123,071)
Interest expense on parent note	(32)	(83)	(61)	(133)
Income (loss) before income taxes	37,843	111,959	297,542	270,889
Income tax (benefit) expense	11,180	31,087	90,941	77,301
Net income (loss)	$ 26,663	$ 80,872	$ 206,601	$ 193,588