CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Electric	$ 1,011,595	$ 944,428	$ 877,967
Gas	245,652	269,871	326,896
Total Revenues	1,257,247	1,214,299	1,204,863
Operating Expenses
Cost of sales	400,973	372,864	482,591
Operating, general and administrative	302,893	297,475	305,886
Property and other taxes	148,098	133,442	114,592
Depreciation and depletion	159,336	144,702	123,776
Total Operating Expenses	1,011,300	948,483	1,026,845
Operating Income	245,947	265,816	178,018
Interest Expense, net	(94,970)	(92,153)	(77,802)
Other Income, net	5,548	7,583	10,198
Income Before Income Taxes	156,525	181,246	110,414
Income Tax Benefit (Expense)	7,647	(30,037)	10,272
Net Income	$ 164,172	$ 151,209	$ 120,686
Average Common Shares Outstanding	48,298,896	47,298,350	40,156,177
Basic Earnings per Average Common Share	$ 3.40	$ 3.20	$ 3.01
Diluted Earnings per Average Common Share	$ 3.39	$ 3.17	$ 2.99