CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Operating revenue:
Electric	$ 469,616	$ 475,580	$ 1,043,243	$ 1,109,133
Gas	184,941	183,935	533,803	571,378
Other	3,784	3,401	8,129	7,780
Total operating revenue	658,341	662,916	1,585,175	1,688,291
Energy costs:
Purchased electricity	104,471	114,627	257,951	295,785
Electric generation fuel	55,652	34,795	103,668	110,232
Residential exchange	(29,054)	(23,621)	(72,768)	(53,624)
Purchased gas	79,465	76,272	235,898	267,578
Unrealized (gain) loss on derivative instruments, net	(8,232)	(17,094)	(11,928)	(24,934)
Utility operations and maintenance	131,972	134,883	269,147	278,960
Non-utility expense and other	2,323	2,293	5,535	5,712
Depreciation	100,412	105,197	206,589	206,916
Conservation amortization	24,561	22,526	54,165	51,508
Taxes other than income taxes	69,999	67,772	164,912	168,590
Total operating expenses	531,569	517,650	1,213,169	1,306,723
Operating income	126,772	145,266	372,006	381,568
Other income (deductions):
Other income	5,255	4,621	10,039	8,863
Other expense	(1,815)	(1,644)	(3,222)	(3,226)
Non-hedged interest rate derivative expense	(1,440)	(1,360)	(3,415)	(2,107)
Interest charges:
AFUDC	1,729	1,562	3,160	2,714
Interest expense	(89,822)	(92,173)	(178,731)	(182,428)
Total before tax	40,679	56,272	199,837	205,384
Tax (expense) or benefit	15,063	15,159	58,545	56,679
Net of Tax	25,616	41,113	141,292	148,705
Subsidiaries [Member]
Operating revenue:
Electric	469,616	475,580	1,043,243	1,109,133
Gas	184,941	183,935	533,803	571,378
Other	3,784	3,401	8,138	7,780
Total operating revenue	658,341	662,916	1,585,184	1,688,291
Energy costs:
Purchased electricity	104,471	114,627	257,951	295,785
Electric generation fuel	55,652	34,795	103,668	110,232
Residential exchange	(29,054)	(23,621)	(72,768)	(53,624)
Purchased gas	79,465	76,272	235,898	267,578
Unrealized (gain) loss on derivative instruments, net	(8,232)	(17,094)	(11,383)	(24,364)
Utility operations and maintenance	131,972	134,883	269,147	278,960
Non-utility expense and other	6,342	5,374	13,349	11,548
Depreciation	100,412	105,197	206,589	206,916
Conservation amortization	24,561	22,526	54,165	51,508
Taxes other than income taxes	69,999	67,772	164,912	168,590
Total operating expenses	535,588	520,731	1,221,528	1,313,129
Operating income	122,753	142,185	363,656	375,162
Other income (deductions):
Other income	5,255	4,621	10,039	8,860
Other expense	(1,815)	(1,644)	(3,222)	(3,226)
Interest charges:
AFUDC	1,729	1,562	3,160	2,714
Interest expense	(62,620)	(65,522)	(125,816)	(129,659)
Interest expense on parent note	(31)	(27)	(63)	(52)
Total before tax	65,271	81,175	247,754	253,799
Tax (expense) or benefit	22,572	23,341	75,955	74,883
Net of Tax	$ 42,699	$ 57,834	$ 171,799	$ 178,916