Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues
Regulated Energy	$ 326,310	$ 305,689	$ 301,902
Unregulated Energy	324,595	203,778	162,108
Other businesses and eliminations	(33,322)	(10,607)	(4,766)
Total operating revenues	617,583	498,860	459,244
Operating Expenses
Regulated Energy cost of sales	118,769	109,609	122,814
Unregulated Energy and other cost of sales	219,145	128,434	97,228
Operations	127,571	117,571	107,562
Maintenance	12,701	12,391	11,803
Gain from a settlement	(130)	(130)	(1,500)
Depreciation and amortization	36,599	32,159	29,972
Other taxes	17,085	14,730	13,607
Total operating expenses	531,740	414,764	381,486
Operating Income	85,843	84,096	77,758
Other (expense) income, net	(765)	(441)	293
Interest charges	12,645	10,639	10,006
Income Before Income Taxes	72,433	73,016	68,045
Income taxes	14,309	28,341	26,905
Net Income	$ 58,124	$ 44,675	$ 41,140
Weighted Average Common Shares Outstanding:
Basic (in shares)	16,336,789	15,570,539	15,094,423
Diluted (in shares)	16,383,352	15,613,091	15,143,373
Earnings Per Share of Common Stock:
Basic (in usd per share)	$ 3.56	$ 2.87	$ 2.73
Diluted (in usd per share)	3.55	2.86	2.72
Cash Dividends Declared Per Share of Common Stock (in usd per share)	$ 1.2800	$ 1.2025	$ 1.1325