CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (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 revenues
Electric	$ 898,811	$ 870,975	$ 2,368,041	$ 2,267,905
Natural gas	137,349	113,230	730,569	643,632
Steam and other	8,140	8,082	29,576	26,303
Total operating revenues	1,044,300	992,287	3,128,186	2,937,840
Operating expenses
Electric fuel and purchased power	355,727	315,319	998,395	920,916
Cost of natural gas sold and transported	43,881	24,662	403,198	338,630
Cost of sales — steam and other	3,398	3,650	12,211	10,745
Operating and maintenance expenses	192,073	180,994	553,266	529,476
Demand side management program expenses	38,016	33,670	104,075	92,462
Depreciation and amortization	88,577	85,905	267,206	249,645
Taxes (other than income taxes)	32,887	32,696	104,120	99,359
Total operating expenses	754,559	676,896	2,442,471	2,241,233
Operating income	289,741	315,391	685,715	696,607
Other income, net	946	1,000	3,845	3,582
Allowance for funds used during construction — equity	8,815	4,687	21,529	10,961
Interest charges and financing costs
Interest charges — includes other financing costs of $1,747, $1,803, $5,118 and $5,383, respectively	43,187	49,369	127,806	145,734
Allowance for funds used during construction — debt	(3,187)	(2,633)	(8,438)	(5,328)
Total interest charges and financing costs	40,000	46,736	119,368	140,406
Income before income taxes	259,502	274,342	591,721	570,744
Income taxes	93,236	81,899	211,551	189,609
Net income	$ 166,266	$ 192,443	$ 380,170	$ 381,135