Commitments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) gal / mo ServiceLine	Mar. 31, 2017 USD ($)
Company-Owned Lead Service Lines [Member]
Commitments [Abstract]
Monthly credit provided to affected customers to flush line | gal / mo	200
Water testing expenses and flushing credits incurred	$ 2	$ 7
Term to replace all remaining company-owned lead service lines	4 years
Costs incurred to replace company-owned lead service lines	$ 1,681
Costs to be incurred to replace company-owned lead service lines	$ 310
Customer-Owned Lead Service Lines [Member]
Commitments [Abstract]
Term of tariff modification to replace customer-owned lead service lines connected to company-owned lead service lines	4 years
Number of lead customer-owned service lines to be replaced annually | ServiceLine	400
Term of tariff modification to replace customer-owned lead service lines regardless of material used for company-owned service lines	9 years
Costs incurred to replace customer-owned lead service lines connected to company-owned lead service lines	$ 221
Costs to be incurred to replace customer-owned lead service lines connected to company-owned lead service lines	40
Costs to be incurred to replace customer-owned lead service lines regardless of the material used for company-owned lead service lines	$ 1,040
Customer-Owned Lead Service Lines [Member] | Minimum [Member]
Commitments [Abstract]
Recovery period of regulatory asset	4 years
Customer-Owned Lead Service Lines [Member] | Maximum [Member]
Commitments [Abstract]
Recovery period of regulatory asset	6 years