Commitments And Contingencies (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 03, 2020	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2020
Commitments And Contingencies [Line Items]
Aggregate amount accrued for loss contingencies			$ 16,917	$ 16,917
Amount probable of recovery through insurance			3,325	3,325
Insurance reserve for employee medical benefit program			1,535	$ 1,535
Insurance proceeds	$ 2,874
Peoples Gas Acquisition [Member]
Commitments And Contingencies [Line Items]
Pipeline term				7 years
Pipeline cost			120,000	$ 120,000
Customer rate credits			23,000	$ 23,000
Customer Rate Credits [Member] | Water And Wastewater Utility Systems [Member]
Commitments And Contingencies [Line Items]
Revenues from contracts with customers			4,080
Customer Rate Credits [Member] | Water And Wastewater Utility Systems [Member] | Peoples Gas Acquisition [Member]
Commitments And Contingencies [Line Items]
Revenues from contracts with customers			$ 4,080
Customer Rate Credits [Member] | Scenario, Forecast [Member] | Peoples Gas Acquisition [Member]
Commitments And Contingencies [Line Items]
Revenues from contracts with customers		$ 23,000
Customer Rate Credits [Member] | Scenario, Forecast [Member] | Natural Gas Utility [Member]
Commitments And Contingencies [Line Items]
Revenues from contracts with customers		$ 18,920