Regulation and Rates (Details) - USD ($) $ in Thousands														3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2020	Jul. 08, 2020	Apr. 06, 2020	Jan. 15, 2020	Nov. 01, 2019	Jun. 20, 2019	Apr. 10, 2019	Mar. 01, 2019	Nov. 07, 2018	May 01, 2018	Mar. 01, 2018	Dec. 19, 2017	Dec. 18, 2017	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Apr. 30, 2019	Jul. 21, 2020	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Regulation and Rates [Line Items]
Income tax (benefit) expense														$ (1,188)	$ 1,481	$ 2,796	$ 9,909
Depreciation & amortization														136,865	164,715	301,681	345,412
Subsidiaries [Member]
Regulation and Rates [Line Items]
Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities									7.49%
Income tax (benefit) expense										$ 34,600				1,999	2,327	15,264	21,157
Annual Power Cost Variability, Interest																1,100	200
PGA payable														86,932	132,766	86,932	132,766	$ 132,766			$ 9,922
Depreciation & amortization														136,816	$ 164,692	301,587	345,370
Liabilities, Other than Long-term Debt, Noncurrent			$ 11,000
Customer Bill Assistance			$ 1
Subsidiaries [Member] | Companys share [Member] | Under-collection [Member]
Regulation and Rates [Line Items]
Annual Power Cost Variability, Amount																48,800	46,400
Subsidiaries [Member] | Customer's share [Member] | Under-collection [Member]
Regulation and Rates [Line Items]
Annual Power Cost Variability, Amount																19,500	17,300
Subsidiaries [Member] | Subsequent Event [Member]
Regulation and Rates [Line Items]
Income tax (benefit) expense		$ 70,800
Liabilities, Other than Long-term Debt, Noncurrent																				$ 4,500
Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Storm Damage Costs Incurred During Period																9,900	39,200
Public Utilities, Rate Case, Deferred Storm Costs Threshold																						$ 10,000	$ 8,000
Public Utilities, Rate Case, Deferred Storm Qualifying Costs																						$ 500
General Rate Case [Member] | Subsidiaries [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Return on Equity, Percentage				9.50%		7.62%
Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities				7.48%					7.49%			7.60%
General Rate Case [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage						6.90%
Public Utilities, Requested Rate Increase (Decrease), Amount				$ (1,500)
General Rate Case [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member] | Subsequent Event [Member]
Regulation and Rates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 31,000	$ 900
Public Utilities, Approved Rate Increase (Decrease), Percentage	1.50%	0.05%
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 59,600	$ 29,500
Public Utilities, Interim Rate Increase (Decrease), Percentage	2.90%	1.60%
Public Utilities Attrition Adjustment Increase Decrease Amount		$ 23,900
PublicUtilitiesIncremenalRateIncreaseDecreaseAmount	$ 30,100
General Rate Case [Member] | Subsidiaries [Member] | Natural Gas, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage						7.90%
General Rate Case [Member] | Subsidiaries [Member] | Natural Gas, US Regulated [Member] | Subsequent Event [Member]
Regulation and Rates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 7,700	$ 1,300
Public Utilities, Approved Rate Increase (Decrease), Percentage	1.00%	0.15%
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 42,900	$ 36,500
Public Utilities, Interim Rate Increase (Decrease), Percentage	5.60%	4.00%
Public Utilities Attrition Adjustment Increase Decrease Amount		$ 16,200
PublicUtilitiesIncremenalRateIncreaseDecreaseAmount	$ 6,400
General Rate Case [Member] | Maximum [Member] | Subsidiaries [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Return on Equity, Percentage						9.80%
General Rate Case [Member] | Maximum [Member] | Subsidiaries [Member] | Subsequent Event [Member]
Regulation and Rates [Line Items]
Public Utilities, Approved Return on Equity, Percentage		9.40%
Public Utilities, Approved Equity Capital Structure, Percentage		48.50%
Public Utilities, Approved Debt Capital Structure, Percentage		7.39%
Public Utilities, Approved Debt Capital Structure, Net of Tax, Percentage		6.80%
Expedited Rate Filing (ERF) [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage									0.90%
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 18,900
Expedited Rate Filing (ERF) [Member] | Subsidiaries [Member] | Natural Gas, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage									2.70%
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 21,700		$ 6,100
Public Utilities, Approved Rate Increase (Decrease), Amount								$ 21,500			$ 25,900
Tax Cuts and Jobs Act [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																			$ (72,900)
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage																			(3.40%)
Contract with Customer, Refund Liability														$ 100		100
Tax Cuts and Jobs Act [Member] | Subsidiaries [Member] | Natural Gas, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																			$ (23,600)
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage																			(2.70%)
Decoupling Mechanism [Member]
Regulation and Rates [Line Items]
Deferred Revenue, Revenue Recognized																0
Decoupling Mechanism [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Contract with Customer, Liability, Revenue Recognized																2,100
Decoupling Mechanism [Member] | Maximum [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage												3.00%
Decoupling Mechanism [Member] | Maximum [Member] | Subsidiaries [Member] | Natural Gas, US Regulated [Member]
Regulation and Rates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage												5.00%	3.00%
General Rate Case, Electric [Member] | Subsidiaries [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage				6.90%
General Rate Case, Natural Gas [Member] | Subsidiaries [Member]
Regulation and Rates [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage				7.90%
Purchased Gas Adjustment [Member] | Subsidiaries [Member]
Regulation and Rates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 17,800
Purchased natural gas costs																169,697		406,162
Purchased natural gas costs, recoverable																(217,916)		(289,876)
Purchased natural gas adjustment, interest																2,385		6,558
Annual revenue					100,600
Out of Cycle PGA					54,000
Under collected commodity balances					114,400
Commodity Costs					10,800
Refund to Customers, remaining balance					4,100
Refund to Customers					$ 54,700
Get to Zero Deferral Filing [Member] | Subsidiaries [Member]
Regulation and Rates [Line Items]
Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities							6.89%
Depreciation & amortization																41,100		21,700
Public Utilities, Property, Plant and Equipment, Equipment, Useful Life							10 years
Carrying charges on deferral																2,000		$ 500
Storm That Occurred In 2018 [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Storm Damage Costs Deferred During Period																	400
Storm That Occurred In 2019 [Member] | Subsidiaries [Member] | Electricity, US Regulated [Member]
Regulation and Rates [Line Items]
Storm Damage Costs Deferred During Period																$ 0	$ 28,300