Fair Value Measurements Valuation Techniques for Measurement with Unobservable Inputs (Details)	3 Months Ended					6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($)		Mar. 31, 2020 USD ($) $ / MWh	Jun. 30, 2019 USD ($)		Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / MWh
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value measurement, sensitivity analysis, hypothetical increase or decrease of market prices, result on fair value	10.00%					10.00%
Fair Value Measurements, Sensitivity Analysis, Hypothetical Increase or Decrease of Market Prices, Result on Fair Value	$ (5,600,000)					$ (5,600,000)		$ (2,500,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	(28,267,000)		$ (25,213,000)	$ (48,000)		(28,267,000)	$ (48,000)	$ (2,096,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	(2,284,000)	[1]		(6,190,000)	[1]	(26,837,000)	6,135,000
Included in regulatory assets/liabilities	(39,000)			382,000		284,000	2,279,000
Settlements	731,000			1,045,000			15,627,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0			0		0
Transferred out of Level 3	0			965,000		0
Rocky Reach
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Finite-Lived Intangible Assets, Net			147,168,000
Impairment of Intangible Assets (Excluding Goodwill)			52,565,000
Asset Impairment Charges			$ 52,600,000
Change in forward prices			7.60%
Rocky Reach | Carrying Value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Finite-lived Intangible Assets, Fair Value Disclosure			$ 94,603,000
Discounted cash flow [Member] | Low [Member] | Rocky Reach
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh			10.23					11.75
Fair Value Inputs, Power Contract Costs			$ 6,308					$ 6,237
Discounted cash flow [Member] | High [Member] | Rocky Reach
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh			29.05					31.44
Fair Value Inputs, Power Contract Costs			$ 7,085					$ 7,087
Discounted cash flow [Member] | Weighted Average [Member] | Rocky Reach
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh			21.27					22.53
Fair Value Inputs, Power Contract Costs			$ 6,468					$ 6,421
Fair Value, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	34,543,000					34,543,000		31,308,000
Derivative Liability	63,941,000					63,941,000		26,121,000
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	1,146,000					1,146,000		2,174,000
Derivative Liability	29,413,000					29,413,000		4,271,000
Electric Portfolio [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	(28,609,000)		$ (26,305,000)	(2,446,000)		(28,609,000)	(2,446,000)	$ (3,378,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	(2,284,000)			(6,190,000)		(26,837,000)	6,135,000
Included in regulatory assets/liabilities	0			0		0	0
Settlements	20,000						12,909,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0			0		0
Transferred out of Level 3	0			1,842,000		$ 0	1,425,000
Electric Portfolio [Member] | Discounted cash flow [Member] | Low [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh)						22.97		9.00
Electric Portfolio [Member] | Discounted cash flow [Member] | High [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh)						40.05		43.85
Electric Portfolio [Member] | Discounted cash flow [Member] | Weighted Average [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh)						30.14		33.99
Electric Portfolio [Member] | Fair Value, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	20,289,000					$ 20,289,000		$ 19,933,000
Derivative Liability	54,238,000					54,238,000		17,504,000
Electric Portfolio [Member] | Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	526,000					526,000		651,000	[2]
Derivative Liability	29,135,000					29,135,000		$ 4,030,000	[2]
Natural Gas Portfolio [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0			0		0	0
Included in regulatory assets/liabilities	(39,000)			382,000		284,000	2,279,000
Settlements	711,000			1,619,000		1,224,000	2,718,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0			$ 0		0	$ (398,000)
Transferred out of Level 3	0					$ 0
Natural Gas Portfolio [Member] | Discounted cash flow [Member] | Low [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MMBtu)						1.10		1.25
Natural Gas Portfolio [Member] | Discounted cash flow [Member] | High [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MMBtu)						3.08		3.18
Natural Gas Portfolio [Member] | Discounted cash flow [Member] | Weighted Average [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MMBtu)						1.78		2.47
Natural Gas Portfolio [Member] | Fair Value, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	14,254,000					$ 14,254,000		$ 11,375,000
Derivative Liability	9,703,000					9,703,000		8,617,000
Natural Gas Portfolio [Member] | Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	620,000					620,000		1,523,000	[2]
Derivative Liability	$ 278,000					$ 278,000		$ 241,000	[2]

[1] Income Statement locations: Unrealized (gain) loss on derivative instruments, net. Amounts include unrealized gains (losses) on derivatives still held in position as of the reporting date for electric derivatives of $(23.1) million and $(4.7) million for three months ended June 30, 2020 and 2019, respectively. ^2. Income Statement locations: Unrealized (gain) loss on derivative instruments, net. Amounts include unrealized gains (losses) on derivatives still held in position as of the reporting date for electric derivatives of $(25.4) million and $(2.4) million for six months ended June 30, 2020 and 2019, respectively.

[2] The valuation techniques, unobservable inputs and ranges are the same for asset and liability positions.