Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues
Total revenues	$ 796,730	$ 854,268	$ 1,580,794	$ 1,669,128
Expenses
Total expenses	714,360	774,862	1,427,767	1,513,906
Operating income (loss)
Total operating income	82,370	79,406	153,027	155,222
Interest expense-other than on deposit liabilities and other bank borrowings	(19,613)	(20,199)	(39,401)	(38,738)
Allowance for borrowed funds used during construction	398	893	1,128	1,763
Allowance for equity funds used during construction	1,560	1,997	2,775	3,937
Income before income taxes	64,715	62,097	117,529	122,184
Income taxes	23,654	22,824	42,316	44,122
Net income	41,061	39,273	75,213	78,062
Preferred stock dividends of subsidiaries	473	473	946	946
Net income for common stock	40,588	38,800	74,267	77,116
Basic earnings per common share (in dollars per share)	$ 0.41	$ 0.40	$ 0.75	$ 0.80
Diluted earnings per common share (in dollars per share)	$ 0.41	$ 0.40	$ 0.75	$ 0.80
Dividends per common share (in dollars per share)	$ 0.31	$ 0.31	$ 0.62	$ 0.62
Weighted-average number of common shares outstanding (in shares)	98,660	96,693	98,399	96,430
Net effect of potentially dilutive shares (in shares)	589	286	562	389
Adjusted weighted-average shares (in shares)	99,249	96,979	98,961	96,819
Electric utility
Revenues
Total revenues	730,688	789,552	1,449,961	1,539,162
Expenses
Total expenses	669,550	728,056	1,335,870	1,420,412
Operating income (loss)
Total operating income	61,138	61,496	114,091	118,750
Income before income taxes	47,517	48,501	86,839	93,708
Income taxes	18,325	18,626	32,719	36,034
Net income	29,192	29,875	54,120	57,674
Preferred stock dividends of subsidiaries	499	499	998	998
Net income for common stock	28,693	29,376	53,122	56,676
Bank
Revenues
Total revenues	66,027	64,721	130,783	129,973
Expenses
Total expenses	41,322	42,847	84,327	85,187
Operating income (loss)
Total operating income	24,705	21,874	46,456	44,786
Income before income taxes	24,705	21,873	46,457	45,337
Income taxes	8,786	7,684	16,383	15,271
Net income	15,919	14,189	30,074	30,066
Net income for common stock	15,919	14,189	30,074	30,066
Other
Revenues
Total revenues	15	(5)	50	(7)
Expenses
Total expenses	3,488	3,959	7,570	8,307
Operating income (loss)
Total operating income	(3,473)	(3,964)	(7,520)	(8,314)
Income before income taxes	(7,507)	(8,277)	(15,767)	(16,861)
Income taxes	(3,457)	(3,486)	(6,786)	(7,183)
Net income	(4,050)	(4,791)	(8,981)	(9,678)
Preferred stock dividends of subsidiaries	(26)	(26)	(52)	(52)
Net income for common stock	$ (4,024)	$ (4,765)	$ (8,929)	$ (9,626)