CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues
Electric	$ 3,115,257	$ 3,125,937	$ 3,081,171
Natural gas	1,006,666	1,215,324	1,080,703
Steam and other	41,590	41,888	40,754
Total operating revenues	4,163,513	4,383,149	4,202,628
Operating expenses
Electric fuel and purchased power	1,246,666	1,405,498	1,335,818
Cost of natural gas sold and transported	501,824	725,754	621,120
Cost of sales — steam and other	17,788	16,831	17,039
Operating and maintenance expenses	761,901	751,786	762,322
Demand side management program expenses	128,681	139,780	139,337
Depreciation and amortization	411,667	379,202	360,417
Taxes (other than income taxes)	195,285	161,928	137,816
Total operating expenses	3,263,812	3,580,779	3,373,869
Operating income	899,701	802,370	828,759
Other income, net	2,964	4,265	3,136
Allowance for funds used during construction — equity	14,485	46,784	33,173
Interest charges and financing costs
Interest charges — includes other financing costs of $6,285, $6,340, and $6,866, respectively	177,430	171,881	173,602
Public Utilities, Allowance For Funds Used During Construction, Capitalized Cost Of Debt	(5,522)	(17,241)	(12,657)
Total interest charges and financing costs	171,908	154,640	160,945
Income before income taxes	745,242	698,779	704,123
Income taxes	278,440	243,591	250,740
Net income	$ 466,802	$ 455,188	$ 453,383