Consolidated Statements of Income (unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenues
Total revenues	$ 637,862	$ 783,749
Expenses
Total expenses	568,356	694,535
Operating income (loss)
Total operating income	69,506	89,214
Interest expense, net—other than on deposit liabilities and other bank borrowings	(19,100)	(19,456)
Allowance for borrowed funds used during construction	499	614
Allowance for equity funds used during construction	1,413	1,609
Income before income taxes	52,318	71,981
Income taxes	19,979	25,721
Net income	32,339	46,260
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	31,866	45,787
Basic earnings per common share (in dollars per share)	$ 0.31	$ 0.45
Diluted earnings per common share (in dollars per share)	$ 0.31	$ 0.45
Dividends per common share (in dollars per share)	$ 0.31	$ 0.31
Weighted-average number of common shares outstanding (in shares)	103,281	101,382
Net effect of potentially dilutive shares (in shares)	286	783
Adjusted weighted-average shares (in shares)	103,567	102,165
Electric utility
Revenues
Total revenues	573,442	720,062
Expenses
Total expenses	515,806	649,396
Operating income (loss)
Total operating income	57,636	70,666
Income before income taxes	43,223	57,166
Income taxes	15,850	21,247
Net income	27,373	35,919
Preferred stock dividends of subsidiaries	499	499
Net income for common stock	26,874	35,420
Bank
Revenues
Total revenues	64,348	63,619
Expenses
Total expenses	43,717	41,088
Operating income (loss)
Total operating income	20,631	22,531
Income before income taxes	20,631	22,532
Income taxes	7,156	8,133
Net income	13,475	14,399
Net income for common stock	13,475	14,399
Other
Revenues
Total revenues	72	68
Expenses
Total expenses	8,833	4,051
Operating income (loss)
Total operating income	(8,761)	(3,983)
Income before income taxes	(11,536)	(7,717)
Income taxes	(3,027)	(3,659)
Net income	(8,509)	(4,058)
Preferred stock dividends of subsidiaries	(26)	(26)
Net income for common stock	$ (8,483)	$ (4,032)