Statements of Consolidated Income shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Operating Revenues:
Utility	$ 453,819	$ 528,763	$ 500,752
Nonutility	582,681	430,805	386,244
Total Operating Revenues	1,036,500	959,568	886,996
Cost of Sales - (Excluding depreciation)
- Utility	167,154	239,763	230,093
- Nonutility	413,833	319,579	306,859
Operations	151,957	148,672	140,260
Maintenance	17,549	16,183	13,457
Depreciation	90,389	72,451	63,004
Energy and Other Taxes	6,342	6,026	5,720
Total Operating Expenses	847,224	802,674	759,393
Operating Income	189,276	156,894	127,603
Other Income and Expense	9,989	9,510	11,819
Interest Charges	(31,449)	(31,622)	(29,560)
Income Before Income Taxes	167,816	134,782	109,862
Income Taxes	(54,151)	(1,360)	(4,449)
Equity in Earnings (Loss) of Affiliated Companies	5,396	(27,812)	(7,785)
Income from Continuing Operations	119,061	105,610	97,628
Loss from Discontinued Operations - (Net of tax benefit)	(251)	(503)	(582)
Net Income	$ 118,810	$ 105,107	$ 97,046
Basic Earnings per Common Share:
Continuing Operations (in USD per share) | $ / shares	$ 1.56	$ 1.54	$ 1.47
Discontinued Operations (in USD per share) | $ / shares	(0.00)	(0.01)	(0.01)
Basic Earnings per Common Share (in USD per share) | $ / shares	$ 1.56	$ 1.53	$ 1.46
Average Shares of Common Stock Outstanding - Basic (in shares) | shares	76,362	68,735	66,278
Diluted Earnings per Common Share:
Continuing Operations (in USD per share) | $ / shares	$ 1.56	$ 1.53	$ 1.47
Discontinued Operations (in USD per share) | $ / shares	(0.00)	(0.01)	(0.01)
Diluted Earnings per Common Share (in USD per share) | $ / shares	$ 1.56	$ 1.52	$ 1.46
Average Shares of Common Stock Outstanding - Diluted (in shares) | shares	76,475	68,931	66,428