Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 2,860,849	$ 2,555,625	$ 2,380,654
Expenses
Total expenses	2,527,493	2,209,392	2,024,816
Operating income (loss)
Operating income	333,356	346,233	355,838
Merger termination fee	0	0	90,000
Retirement defined benefits expense—other than service costs	(5,962)	(7,942)	(7,663)
Interest expense, net – other than on deposit liabilities and other bank borrowings	(88,677)	(78,972)	(75,803)
Allowance for borrowed funds used during construction	4,867	4,778	3,144
Allowance for equity funds used during construction	10,877	12,483	8,325
Income before income taxes	254,461	276,580	373,841
Income taxes	50,797	109,393	123,695
Net income (loss)	203,664	167,187	250,146
Preferred stock dividends of subsidiaries	1,890	1,890	1,890
Net income for common stock	$ 201,774	$ 165,297	$ 248,256
Basic earnings per common share (in dollars per share)	$ 1.85	$ 1.52	$ 2.30
Diluted earnings per common share (in dollars per share)	$ 1.85	$ 1.52	$ 2.29
Weighted-average number of common shares outstanding (in shares)	108,855	108,749	108,102
Net effect of potentially dilutive shares (in shares)	291	184	207
Weighted-average shares assuming dilution (in shares)	109,146	108,933	108,309
Electric utility
Revenues
Revenues	$ 2,546,525	$ 2,257,566	$ 2,094,368
Expenses
Total expenses	2,304,864	1,994,042	1,804,298
Operating income (loss)
Operating income	241,661	263,524	290,070
Income before income taxes	180,426	205,145	229,113
Income taxes	34,778	83,199	84,801
Net income (loss)	145,648	121,946	144,312
Preferred stock dividends of subsidiaries	1,995	1,995	1,995
Net income for common stock	143,653	119,951	142,317
Bank
Revenues
Revenues	314,275	297,640	285,924
Expenses
Total expenses	206,040	198,104	197,697
Operating income (loss)
Operating income	108,235	99,536	88,227
Income before income taxes	106,578	98,716	87,352
Income taxes	24,069	31,719	30,073
Net income (loss)	82,509	66,997	57,279
Preferred stock dividends of subsidiaries	0	0	0
Net income for common stock	82,509	66,997	57,279
Other
Revenues
Revenues	49	419	362
Expenses
Total expenses	16,589	17,246	22,821
Operating income (loss)
Operating income	(16,540)	(16,827)	(22,459)
Income before income taxes	(32,543)	(27,281)	57,376
Income taxes	(8,050)	(5,525)	8,821
Net income (loss)	(24,493)	(21,756)	48,555
Preferred stock dividends of subsidiaries	(105)	(105)	(105)
Net income for common stock	$ (24,388)	$ (21,651)	$ 48,660