Income Taxes (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Position	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Provisions for Income Taxes [Abstract]
Federal current	$ 2,681	$ 1,873	$ 96
State current	1,082	597	28
Federal deferred	1,683	2,131	3,757
State deferred	2	177	1,035
Federal investment tax credit, net of current utilization	(39)	(38)	(39)
Total income taxes	$ 5,409	$ 4,740	$ 4,877
Reconciliation of Statutory Federal Tax Provision to Total Provision [Abstract]
Statutory Federal tax percentage	34.00%	34.00%	34.00%
Statutory Federal tax provision	$ 5,867	$ 5,858	$ 5,563
State income taxes, net of Federal benefit	715	511	702
IRS TPR ongoing deduction	(962)	(1,438)	(1,342)
Tax-exempt interest	(34)	(37)	(37)
Amortization of investment tax credit	(39)	(38)	(39)
Cash value of life insurance	44	71	15
Domestic production deduction	(194)	(190)	0
Other, net	12	3	15
Total income taxes	5,409	4,740	4,877
Regulatory Liabilities [Abstract]
Regulatory liabilities	4,640	4,663
Deferred Tax Assets [Abstract]
Reserve for doubtful accounts	124	128
Compensated absences	212	221
Deferred compensation	1,581	1,465
Customers' advances and contributions	0	1
Deferred taxes associated with the gross-up of revenues necessary to return, in rates, the effect of temporary differences	124	122
Pensions	2,146	3,099
Contribution carryover	0	147
Other costs deducted for book, not for tax	57	51
Total deferred tax assets	4,244	5,234
Deferred Tax Liabilities [Abstract]
Accelerated depreciation	38,063	36,210
Basis differences from IRS TPR	8,339	7,196
Investment tax credit	390	413
Deferred taxes associated with the gross-up of revenues necessary to recover, in rates, the effect of temporary differences	8,183	7,271
Tax effect of pension regulatory asset	3,033	3,986
Other costs deducted for tax, not for book	405	438
Total deferred tax liabilities	58,413	55,514
Net deferred tax liability	54,169	50,280
Other Income Tax Disclosures [Abstract]
Uncertain tax positions	$ 0
Number of new tax positions taken | Position	0
Interest or penalties	$ 0	0	0
Maximum [Member]
Other Income Tax Disclosures [Abstract]
Open tax year	2015
Minimum [Member]
Other Income Tax Disclosures [Abstract]
Open tax year	2013
Valuation Allowance of Deferred Tax Assets [Member]
Other Income Tax Disclosures [Abstract]
Valuation allowance	$ 0	0
IRS TPR Catch-Up Deduction [Member]
Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 3,887	$ 3,887	$ 4,314