Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues
Total revenues	$ 798,657	$ 794,567	$ 1,582,406	$ 1,576,799
Expenses
Total expenses	716,382	714,360	1,411,825	1,427,767
Operating income (loss)
Total operating income	82,275	80,207	170,581	149,032
Interest expense, net—other than on deposit liabilities and other bank borrowings	(20,022)	(18,442)	(39,478)	(37,173)
Allowance for borrowed funds used during construction	523	398	1,137	1,128
Allowance for equity funds used during construction	1,387	1,560	2,996	2,775
Income before income taxes	64,163	63,723	135,236	115,762
Income taxes	22,269	22,662	46,942	40,549
Net income	41,894	41,061	88,294	75,213
Preferred stock dividends of subsidiaries	473	473	946	946
Net income for common stock	41,421	40,588	87,348	74,267
Basic earnings per common share (in dollars per share)	$ 0.41	$ 0.41	$ 0.86	$ 0.75
Diluted earnings per common share (in dollars per share)	$ 0.41	$ 0.41	$ 0.86	$ 0.75
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)	101,495	98,660	101,439	98,399
Net effect of potentially dilutive shares (in shares)	330	589	606	562
Adjusted weighted-average shares (in shares)	101,825	99,249	102,045	98,961
Electric utility
Revenues
Total revenues	738,429	728,525	1,458,491	1,445,966
Expenses
Total expenses	668,361	669,550	1,317,757	1,335,870
Operating income (loss)
Total operating income	70,068	58,975	140,734	110,096
Income before income taxes	55,126	46,525	112,292	85,072
Income taxes	20,397	17,333	41,644	30,952
Net income	34,729	29,192	70,648	54,120
Preferred stock dividends of subsidiaries	499	499	998	998
Net income for common stock	34,230	28,693	69,650	53,122
Bank
Revenues
Total revenues	60,616	66,027	124,235	130,783
Expenses
Total expenses	43,568	41,322	85,564	84,327
Operating income (loss)
Total operating income	17,048	24,705	38,671	46,456
Income before income taxes	17,048	24,705	38,672	46,457
Income taxes	5,372	8,786	12,457	16,383
Net income	11,676	15,919	26,215	30,074
Net income for common stock	11,676	15,919	26,215	30,074
Other
Revenues
Total revenues	(388)	15	(320)	50
Expenses
Total expenses	4,453	3,488	8,504	7,570
Operating income (loss)
Total operating income	(4,841)	(3,473)	(8,824)	(7,520)
Income before income taxes	(8,011)	(7,507)	(15,728)	(15,767)
Income taxes	(3,500)	(3,457)	(7,159)	(6,786)
Net income	(4,511)	(4,050)	(8,569)	(8,981)
Preferred stock dividends of subsidiaries	(26)	(26)	(52)	(52)
Net income for common stock	$ (4,485)	$ (4,024)	$ (8,517)	$ (8,929)