CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues
Electric	$ 3,081,171	$ 2,969,899	$ 3,114,370
Natural gas	1,080,703	962,435	1,087,749
Steam and other	40,754	36,959	38,683
Total operating revenues	4,202,628	3,969,293	4,240,802
Operating expenses
Electric fuel and purchased power	1,335,818	1,235,343	1,425,173
Cost of natural gas sold and transported	621,120	532,417	692,096
Cost of sales — steam and other	17,039	15,438	17,552
Operating and maintenance expenses	762,322	742,975	734,729
Demand side management program expenses	139,337	123,205	115,078
Depreciation and amortization	360,417	338,827	328,582
Taxes (other than income taxes)	137,816	131,869	133,660
Total operating expenses	3,373,869	3,120,074	3,446,870
Operating income	828,759	849,219	793,932
Other income, net	3,136	4,736	7,001
Allowance for funds used during construction — equity	33,173	16,354	7,710
Interest charges and financing costs
Interest charges — includes other financing costs of $6,866, $7,088, and $6,883, respectively	173,602	188,094	186,885
Allowance for funds used during construction — debt	(12,657)	(8,405)	(3,406)
Total interest charges and financing costs	160,945	179,689	183,479
Income before income taxes	704,123	690,620	625,164
Income taxes	250,740	232,544	228,361
Net income	$ 453,383	$ 458,076	$ 396,803