Statements of Consolidated Income shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Operating Revenues:
Utility	$ 528,763	$ 500,752	$ 444,920
Nonutility	430,805	386,244	286,501
Total Operating Revenues	959,568	886,996	731,421
Cost of Sales - (Excluding depreciation)
- Utility	239,763	230,093	198,521
- Nonutility	319,579	306,859	270,470
Operations	148,672	140,260	120,205
Maintenance	16,183	13,457	13,136
Depreciation	72,451	63,004	49,637
Energy and Other Taxes	6,026	5,720	9,816
Total Operating Expenses	802,674	759,393	661,785
Operating Income	156,894	127,603	69,636
Other Income and Expense	9,510	11,819	10,979
Interest Charges	(31,622)	(29,560)	(18,825)
Income Before Income Taxes	134,782	109,862	61,790
Income Taxes	(1,360)	(4,449)	19,014
Equity in (Loss) Earnings of Affiliated Companies	(27,812)	(7,785)	1,585
Income from Continuing Operations	105,610	97,628	82,389
Loss from Discontinued Operations - (Net of tax benefit)	(503)	(582)	(796)
Net Income	$ 105,107	$ 97,046	$ 81,593
Basic Earnings per Common Share:
Continuing Operations (in USD per share) | $ / shares	$ 1.54	$ 1.47	$ 1.29
Discontinued Operations (in USD per share) | $ / shares	(0.01)	(0.01)	(0.01)
Basic Earnings per Common Share (in USD per share) | $ / shares	$ 1.53	$ 1.46	$ 1.28
Average Shares of Common Stock Outstanding - Basic (in shares) | shares	68,735	66,278	63,978
Diluted Earnings per Common Share:
Continuing Operations (in USD per share) | $ / shares	$ 1.53	$ 1.47	$ 1.29
Discontinued Operations (in USD per share) | $ / shares	(0.01)	(0.01)	(0.01)
Diluted Earnings per Common Share (in USD per share) | $ / shares	$ 1.52	$ 1.46	$ 1.28
Average Shares of Common Stock Outstanding - Diluted (in shares) | shares	68,931	66,428	64,092