Acquisition (Details) people in Thousands, $ in Thousands	Jun. 01, 2020 USD ($) waterSystem people customerConnection	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 30,349	$ 2,615
Rainier View Water Company
Business Acquisition [Line Items]
Number of people served | people	35
Number of customer connections | customerConnection	18,500
Water systems | waterSystem	27
Rainier View Water Company
Business Acquisition [Line Items]
Cash paid	$ 37,600
Assets acquired and liabilities assumed	32,700
Assets acquired and liabilities assumed, property, plant, and equipment	31,100
Recognized identifiable assets acquired and liabilities assumed, liabilities	22,900
Recognized identifiable assets acquired and liabilities assumed, aid for construction	21,300
Goodwill	$ 27,700