CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Operating Revenues	$ 132,906	$ 126,025	$ 117,139
Operating Expenses:
Operations and Maintenance	65,534	65,167	59,129
Depreciation	12,796	12,051	11,444
Other Taxes	13,944	12,967	12,174
Total Operating Expenses	92,274	90,185	82,747
Operating Income	40,632	35,840	34,392
Other Income (Expense):
Allowance for Funds Used During Construction	619	380	317
Other Income	662	208	281
Other Expense	(2,143)	(295)	(1,001)
Total Other Income (Expense), net	(862)	293	(403)
Interest Charges	5,293	5,554	5,607
Income before Income Taxes	34,477	30,579	28,382
Income Taxes	11,735	10,551	9,937
Net Income	22,742	20,028	18,445
Preferred Stock Dividend Requirements	144	144	151
Earnings Applicable to Common Stock	$ 22,598	$ 19,884	$ 18,294
Earnings per share of Common Stock:
Basic	$ 1.39	$ 1.23	$ 1.14
Diluted	$ 1.38	$ 1.22	$ 1.13
Average Number of Common Shares Outstanding :
Basic	16,270,000	16,175,000	16,052,000
Diluted	16,426,000	16,331,000	16,226,000
Cash Dividends Paid per Common Share	$ 0.808	$ 0.776	$ 0.763