CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenue:
Electric	$ 477,483	$ 455,726	$ 1,553,774	$ 1,537,764
Gas	120,796	123,984	686,289	767,773
Other	69	(955)	589	347
Total operating revenue	598,348	578,755	2,240,652	2,305,884
Energy costs:
Purchased electricity	92,774	85,933	380,360	441,145
Electric generation fuel	76,689	64,798	176,513	154,596
Residential exchange	(13,949)	(14,038)	(51,464)	(52,675)
Purchased gas	45,889	51,311	315,359	381,291
Unrealized (gain) loss on derivative instruments, net	(8,888)	(67,490)	(57,203)	(126,840)
Utility operations and maintenance	129,963	120,386	389,484	376,627
Non-utility expense and other	(1,640)	(54)	(3,592)	738
Depreciation	91,834	85,314	270,314	248,872
Amortization	5,365	16,491	17,542	41,381
Conservation amortization	20,645	20,650	77,220	83,570
Taxes other than income taxes	59,623	62,192	213,260	235,021
Total operating expenses	498,305	425,493	1,727,793	1,783,726
Operating income	100,043	153,262	512,859	522,158
Other income (deductions):
Other income	9,197	6,891	32,052	40,165
Other expense	(1,844)	(2,775)	(4,840)	(8,475)
Non-hedged interest rate derivative expense	(470)	1,512	1,790	(5,258)
Interest charges:
AFUDC	2,338	5,252	10,148	17,234
Interest expense	(94,788)	(96,507)	(299,521)	(299,672)
Income (loss) before income taxes	14,476	67,635	252,488	266,152
Income tax (benefit) expense	5,936	20,943	75,569	73,289
Net income (loss)	8,540	46,692	176,919	192,863
Subsidiaries [Member]
Operating revenue:
Electric	477,483	455,726	1,553,774	1,537,764
Gas	120,796	123,984	686,289	767,773
Other	69	(99)	479	1,203
Total operating revenue	598,348	579,611	2,240,542	2,306,740
Energy costs:
Purchased electricity	92,774	85,933	380,360	441,145
Electric generation fuel	76,689	64,798	176,513	154,596
Residential exchange	(13,949)	(14,038)	(51,464)	(52,675)
Purchased gas	45,889	51,311	315,359	381,291
Unrealized (gain) loss on derivative instruments, net	(8,888)	(65,594)	(54,252)	(115,309)
Utility operations and maintenance	129,963	120,386	389,484	376,627
Non-utility expense and other	2,318	2,161	8,439	7,665
Depreciation	91,834	85,314	270,314	248,872
Amortization	5,365	16,491	17,542	41,381
Conservation amortization	20,645	20,650	77,220	83,570
Taxes other than income taxes	59,623	62,192	213,260	235,021
Total operating expenses	502,263	429,604	1,742,775	1,802,184
Operating income	96,085	150,007	497,767	504,556
Other income (deductions):
Other income	9,197	6,891	32,051	40,153
Other expense	(1,844)	(2,775)	(4,840)	(8,475)
Interest charges:
AFUDC	2,338	5,252	10,148	17,234
Interest expense	(64,614)	(61,524)	(196,363)	(184,595)
Interest expense on parent note	(27)	(34)	(88)	(167)
Income (loss) before income taxes	41,135	97,817	338,675	368,706
Income tax (benefit) expense	14,530	30,949	105,470	108,250
Net income (loss)	$ 26,605	$ 66,868	$ 233,205	$ 260,456