Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Revenues
Total revenues	$ 784,064	$ 814,860
Expenses
Total expenses	713,407	739,044
Operating income (loss)
Total operating income	70,657	75,816
Interest expense-other than on deposit liabilities and other bank borrowings	(19,788)	(18,539)
Allowance for borrowed funds used during construction	730	870
Allowance for equity funds used during construction	1,215	1,940
Income before income taxes	52,814	60,087
Income taxes	18,662	21,298
Net income	34,152	38,789
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	33,679	38,316
Basic earnings per common share (in dollars per share)	$ 0.34	$ 0.40
Diluted earnings per common share (in dollars per share)	$ 0.34	$ 0.40
Dividends per common share (in dollars per share)	$ 0.31	$ 0.31
Weighted-average number of common shares outstanding (in shares)	98,135	96,167
Net effect of potentially dilutive shares (in shares)	405	394
Adjusted weighted-average shares (in shares)	98,540	96,561
Electric utility
Revenues
Total revenues	719,273	749,610
Expenses
Total expenses	666,320	692,356
Operating income (loss)
Total operating income	52,953	57,254
Income before income taxes	39,322	45,207
Income taxes	14,394	17,408
Net income	24,928	27,799
Preferred stock dividends of subsidiaries	499	499
Net income for common stock	24,429	27,300
Bank
Revenues
Total revenues	64,756	65,252
Expenses
Total expenses	43,005	42,340
Operating income (loss)
Total operating income	21,751	22,912
Income before income taxes	21,752	23,464
Income taxes	7,597	7,587
Net income	14,155	15,877
Net income for common stock	14,155	15,877
Other
Revenues
Total revenues	35	(2)
Expenses
Total expenses	4,082	4,348
Operating income (loss)
Total operating income	(4,047)	(4,350)
Income before income taxes	(8,260)	(8,584)
Income taxes	(3,329)	(3,697)
Net income	(4,931)	(4,887)
Preferred stock dividends of subsidiaries	(26)	(26)
Net income for common stock	$ (4,905)	$ (4,861)