Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) System	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Significant Accounting Policies [Abstract]
Number of wastewater collection and treatment systems operated | System	2
Utility Plant and Depreciation [Abstract]
Utility plant acquisition adjustments	$ 3,667	$ 3,724
Amortization of utility plant acquisition adjustments	58	58	$ 54
Utility Plant	$ 343,412	$ 329,415
Effective rate of depreciation	2.25%	2.24%	2.26%
Assets [Abstract]
Regulatory assets	$ 33,027	$ 32,996
Liabilities [Abstract]
Regulatory liabilities	4,640	4,663
Interest Rate Swap Agreement [Abstract]
Interest rate swap settlements reclassified from regulatory assets to interest expense	345	366	$ 368
Interest rate swap (gain) loss capitalized	128	285	$ 1,318
Interest rate swap settlements to be reclassified during the next 12 months	$ 310
Interest rate swap expire period	Oct. 01, 2029
Income Taxes [Abstract]
Deferred investment tax credits	$ 657	$ 696
Allowance for Funds Used During Construction [Abstract]
PPUC approved rate for AFUDC	10.04%	10.04%	10.04%
Minimum [Member]
Allowance for Funds Used During Construction [Abstract]
Allowance for tax-exempt funds rate used during construction		4.00%
Maximum [Member]
Allowance for Funds Used During Construction [Abstract]
Allowance for tax-exempt funds rate used during construction		4.50%
IRS TPR Catch-Up Deduction [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 3,887	$ 3,887	$ 4,314
Income Taxes [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 753	776
Income Taxes [Member] | Minimum [Member]
Liabilities [Abstract]
Remaining recovery periods	1 year
Income Taxes [Member] | Maximum [Member]
Liabilities [Abstract]
Remaining recovery periods	50 years
Income Taxes [Member]
Assets [Abstract]
Regulatory assets	$ 20,609	18,389
Postretirement Benefits [Member]
Assets [Abstract]
Regulatory assets	$ 7,471	9,819
Postretirement Benefits [Member] | Minimum [Member]
Assets [Abstract]
Remaining recovery periods	5 years
Postretirement Benefits [Member] | Maximum [Member]
Assets [Abstract]
Remaining recovery periods	10 years
Unrealized Swap Losses [Member]
Assets [Abstract]
Regulatory assets	$ 2,264	2,481
Unrealized Swap Losses [Member] | Minimum [Member]
Assets [Abstract]
Remaining recovery periods	1 year
Unrealized Swap Losses [Member] | Maximum [Member]
Assets [Abstract]
Remaining recovery periods	13 years
Utility Plant Retirement Costs [Member]
Assets [Abstract]
Regulatory assets	$ 2,679	2,247
Remaining recovery periods	5 years
Service Life Study Expenses [Member]
Assets [Abstract]
Regulatory assets	$ 4	3
Remaining recovery periods	1 year
Rate Case Filing Expenses [Member]
Assets [Abstract]
Regulatory assets	$ 0	57
Mains and Accessories [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 176,068	170,991
Mains and Accessories [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	10 years
Mains and Accessories [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	83 years
Services, Meters and Hydrants [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 68,510	66,267
Services, Meters and Hydrants [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	19 years
Services, Meters and Hydrants [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	54 years
Operations Structures, Reservoirs and Water Tanks [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 46,494	44,739
Operations Structures, Reservoirs and Water Tanks [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	11 years
Operations Structures, Reservoirs and Water Tanks [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	37 years
Pumping and Treatment Equipment [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 29,459	27,664
Pumping and Treatment Equipment [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	2 years
Pumping and Treatment Equipment [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	33 years
Office, Transportation and Operating Equipment [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 12,360	11,725
Office, Transportation and Operating Equipment [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	3 years
Office, Transportation and Operating Equipment [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Approximate range of remaining lives	20 years
Land and Other Non-Depreciable Assets [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 3,172	3,172
Approximate range of remaining lives	0 years
Utility Plant in Service [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 336,063	324,558
Construction Work in Progress [Member]
Utility Plant and Depreciation [Abstract]
Utility Plant	$ 7,349	4,857
Approximate range of remaining lives	0 years
Accounting Standards Update 2015-17 [Member]
Impact of Recent Accounting Pronouncements [Abstract]
Deferred income taxes		215
Accounting Standards Update 2015-03 [Member]
Impact of Recent Accounting Pronouncements [Abstract]
Deferred debt expense		$ 2,743