Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Revenues
Total revenues	$ 814,860	$ 710,633
Expenses
Total expenses	739,044	647,258
Operating income (loss)
Total operating income	75,816	63,375
Interest expense-other than on deposit liabilities and other bank borrowings	(18,539)	(20,140)
Allowance for borrowed funds used during construction	870	520
Allowance for equity funds used during construction	1,940	1,244
Income before income taxes	60,087	44,999
Income taxes	21,298	16,064
Net income	38,789	28,935
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	38,316	28,462
Basic earnings per common share (in dollars per share)	$ 0.40	$ 0.30
Diluted earnings per common share (in dollars per share)	$ 0.40	$ 0.30
Dividends per common share (in dollars per share)	$ 0.31	$ 0.31
Weighted-average number of common shares outstanding (in shares)	96,167	94,817
Dilutive effect of share-based compensation (in shares)	394	365
Adjusted weighted-average shares (in shares)	96,561	95,182
Electric utility
Revenues
Total revenues	749,610	645,335
Expenses
Total expenses	692,356	600,127
Operating income (loss)
Total operating income	57,254	45,208
Income before income taxes	45,207	31,267
Income taxes	17,408	11,579
Net income	27,799	19,688
Preferred stock dividends of subsidiaries	499	499
Net income for common stock	27,300	19,189
Bank
Revenues
Total revenues	65,252	65,313
Expenses
Total expenses	42,340	43,559
Operating income (loss)
Total operating income	22,912	21,754
Income before income taxes	23,464	21,727
Income taxes	7,587	7,876
Net income	15,877	13,851
Net income for common stock	15,877	13,851
Other
Revenues
Total revenues	(2)	(15)
Expenses
Total expenses	4,348	3,572
Operating income (loss)
Total operating income	(4,350)	(3,587)
Income before income taxes	(8,584)	(7,995)
Income taxes	(3,697)	(3,391)
Net income	(4,887)	(4,604)
Preferred stock dividends of subsidiaries	(26)	(26)
Net income for common stock	$ (4,861)	$ (4,578)