Significant Accounting Policies, Utility Plant and Depreciation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) System	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Abstract]
Number of wastewater collection and treatment systems operated | System	3
Utility Plant and Depreciation [Abstract]
Utility plant acquisition adjustments	$ 3,234	$ 3,667
Amortization of utility plant acquisition adjustments	58	58	$ 58
Utility plant	$ 365,767	$ 343,412
Effective rate of depreciation	2.26%	2.25%	2.24%
Mains and Accessories [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 182,927	$ 176,068
Mains and Accessories [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	10 years
Mains and Accessories [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	83 years
Services, Meters and Hydrants [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 71,183	68,510
Services, Meters and Hydrants [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	19 years
Services, Meters and Hydrants [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	54 years
Operations Structures, Reservoirs and Water Tanks [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 53,610	46,494
Operations Structures, Reservoirs and Water Tanks [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	11 years
Operations Structures, Reservoirs and Water Tanks [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	37 years
Pumping and Treatment Equipment [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 29,814	29,459
Pumping and Treatment Equipment [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	2 years
Pumping and Treatment Equipment [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	33 years
Office, Transportation and Operating Equipment [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 12,787	12,360
Office, Transportation and Operating Equipment [Member] | Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	3 years
Office, Transportation and Operating Equipment [Member] | Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	20 years
Land and Other Non-Depreciable Assets [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 3,196	3,172
Utility Plant in Service [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	353,517	336,063
Construction Work in Progress [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 12,250	$ 7,349