Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues
Total revenues	$ 3,242,335	$ 2,664,982	$ 2,309,590
Expenses
Total expenses	2,952,639	2,408,771	2,121,926
Operating income (loss)
Total operating income (loss)	289,696	256,211	187,664
Interest expense - other than on deposit liabilities and other bank borrowings	(82,106)	(81,538)	(76,330)
Allowance for borrowed funds used during construction	2,498	2,558	5,268
Allowance for equity funds used during construction	5,964	6,016	12,222
Income before income taxes	216,052	183,247	128,824
Income taxes	75,932	67,822	43,923
Net income	140,120	115,425	84,901
Preferred stock dividends of subsidiaries	1,890	1,890	1,890
Net income for common stock	138,230	113,535	83,011
Basic earnings per common share (in dollars per share)	$ 1.45	$ 1.22	$ 0.91
Diluted earnings per common share (in dollars per share)	$ 1.44	$ 1.21	$ 0.91
Dividends per common share (in dollars per share)	$ 1.24	$ 1.24	$ 1.24
Weighted-average number of common shares outstanding	95,510	93,421	91,396
Dilutive effect of share-based compensation (in shares)	310	272	120
Adjusted weighted-average shares	95,820	93,693	91,516
Electric utility
Revenues
Total revenues	2,978,690	2,382,366	2,035,009
Expenses
Total expenses	2,763,556	2,203,978	1,865,338
Operating income (loss)
Total operating income (loss)	215,134	178,388	169,671
Income before income taxes	163,565	125,452	129,217
Income taxes	61,584	46,868	47,776
Net income	101,981	78,584	81,441
Preferred stock dividends of subsidiaries	1,995	1,995	1,995
Net income for common stock	99,986	76,589	79,446
Bank
Revenues
Total revenues	264,407	282,693	274,719
Expenses
Total expenses	172,806	190,105	242,955
Operating income (loss)
Total operating income (loss)	91,601	92,588	31,764
Income before income taxes	91,536	92,512	31,705
Income taxes	31,693	34,056	9,938
Net income	59,843	58,456	21,767
Net income for common stock	59,843	58,456	21,767
Other
Revenues
Total revenues	(762)	(77)	(138)
Expenses
Total expenses	16,277	14,688	13,633
Operating income (loss)
Total operating income (loss)	(17,039)	(14,765)	(13,771)
Income before income taxes	(39,049)	(34,717)	(32,098)
Income taxes	(17,345)	(13,102)	(13,791)
Net income	(21,704)	(21,615)	(18,307)
Preferred stock dividends of subsidiaries	(105)	(105)	(105)
Net income for common stock	$ (21,599)	$ (21,510)	$ (18,202)