Narrative (Details) - USD ($)					6 Months Ended	12 Months Ended
	Nov. 01, 2019	Apr. 10, 2019	Nov. 07, 2018	Dec. 19, 2017	Dec. 31, 2013	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Jan. 01, 2017
Regulatory Assets [Line Items]
Depreciation and amortization						$ 656,323,000	$ 666,432,000	$ 481,969,000
Accrual for Environmental Loss Contingencies						31.6
Subsidiaries [Member]
Regulatory Assets [Line Items]
Storm Damage Costs Incurred During Period						39,300,000	25,400,000
PGA payable								16,100,000
Depreciation and amortization						656,220,000	666,324,000	$ 481,955,000
Purchased gas adjustment receivable						132,800,000	9,900,000
Public Utilities, Rate Case, Deferred Storm Costs Threshold									$ 10,000,000.0	$ 8,000,000.0
Public Utilities, Rate Case, Deferred Storm Qualifying Costs									$ 0.5
Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities			7.49%	7.60%	7.77%
Subsidiaries [Member] | Purchased Gas Adjustment [Member]
Regulatory Assets [Line Items]
Purchased natural gas costs, recoverable						292,000,000.0	289,900,000
Purchased natural gas adjustment, interest						1,300,000	6,600,000
Out of Cycle PGA	$ 54,000,000.0
purchased gas costs						319,300,000	406,200,000
Commodity Costs	10,800,000
Under collected commodity balances	114,400,000
Public Utilities, Approved Rate Increase (Decrease), Amount	17,800,000
Annual revenue	100,600,000
Refund to Customers	54,700,000
Refund to Customers, remaining balance	$ 4,100,000
Subsidiaries [Member] | Get to Zero Deferral Filing [Member]
Regulatory Assets [Line Items]
Depreciation and amortization		$ 21,700,000
Carrying charges on deferral		$ 500,000
Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities		6.89%
Public Utilities, Property, Plant and Equipment, Equipment, Useful Life		10 years
Subsidiaries [Member] | Storm that occurred in 2019 [Member]
Regulatory Assets [Line Items]
Storm Damage Costs Deferred During Period						28,500,000
Subsidiaries [Member] | Storm that occurred in 2018 [Member]
Regulatory Assets [Line Items]
Storm Damage Costs Deferred During Period						400,000	11,900,000
Subsidiaries [Member] | Storm that occurred in 2017 [Member]
Regulatory Assets [Line Items]
Storm Damage Costs Deferred During Period							3,300,000
Natural Gas, US Regulated [Member]
Regulatory Assets [Line Items]
Environmental Expense and Liabilities						54,800,000	62,200,000
Environmental Remediation Expense						41,800,000
Electricity, US Regulated [Member]
Regulatory Assets [Line Items]
Environmental Expense and Liabilities						13,700,000	$ 14,100,000
Environmental Remediation Expense						$ 8,700,000