CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues
Electric	$ 3,049,352	$ 3,115,257	$ 3,125,937
Natural gas	957,721	1,006,666	1,215,324
Steam and other	40,723	41,590	41,888
Total operating revenues	4,047,796	4,163,513	4,383,149
Operating expenses
Electric fuel and purchased power	1,196,417	1,246,666	1,405,498
Cost of natural gas sold and transported	425,410	501,824	725,754
Cost of sales — steam and other	15,872	17,788	16,831
Operating and maintenance expenses	762,416	761,901	751,786
Demand side management program expenses	118,175	128,681	139,780
Depreciation and amortization	443,555	411,667	379,202
Taxes (other than income taxes)	196,330	195,285	161,928
Total operating expenses	3,158,175	3,263,812	3,580,779
Operating income	889,621	899,701	802,370
Other income, net	3,817	2,964	4,265
Allowance for funds used during construction — equity	18,557	14,485	46,784
Interest charges and financing costs
Interest charges — includes other financing costs of $6,289, $6,285 and $6,340, respectively	181,631	177,430	171,881
Public Utilities, Allowance For Funds Used During Construction, Capitalized Cost Of Debt	(7,045)	(5,522)	(17,241)
Total interest charges and financing costs	174,586	171,908	154,640
Income before income taxes	737,409	745,242	698,779
Income taxes	273,918	278,440	243,591
Net income	$ 463,491	$ 466,802	$ 455,188