Fair Value Measurements Valuation Techniques for Measurement with Unobservable Inputs (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) $ / MWh	Sep. 30, 2021 USD ($) $ / MWh $ / MMBTU	Dec. 31, 2020 USD ($) $ / MWh $ / MMBTU
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		0.10%
Fair Value Measurements, Sensitivity Analysis, Hypothetical Increase or Decrease of Market Prices, Result on Fair Value		$ 8,400,000	$ 5,500,000
Impairment of Intangible Assets, Finite-lived		0
Wells Project
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
Wells Project | 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
Fair Value Inputs, Power Contract Costs	$ 6,308,000
Discounted cash flow [Member] | High [Member] | Wells Project
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh	38.84
Discounted cash flow [Member] | High [Member] | Rocky Reach
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Power Contract Costs	$ 7,085,000
Discounted cash flow [Member] | Weighted Average [Member] | Wells Project
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh	24.43
Discounted cash flow [Member] | Weighted Average [Member] | Rocky Reach
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Power Contract Costs	$ 6,468,000
Fair Value, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		362,527,000	41,820,000
Derivative Liability		62,454,000	61,274,000
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		15,834,000	734,000
Derivative Liability		$ 6,090,000	$ 25,587,000
Electric Portfolio [Member] | Discounted cash flow [Member] | Low [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh		34.50	22.82
Electric Portfolio [Member] | Discounted cash flow [Member] | High [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh		95.61	41.66
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) | $ / MWh		53.50	31.54
Electric Portfolio [Member] | Fair Value, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		$ 193,765,000	$ 22,544,000
Derivative Liability		45,349,000	46,922,000
Electric Portfolio [Member] | Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		15,762,000	597,000
Derivative Liability		4,334,000	24,315,000
Electric Portfolio [Member] | Fair Value, Recurring [Member] | Parent Company [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		15,762,000	597,000
Derivative Liability		$ 4,334,000	$ 24,315,000
Natural Gas Portfolio [Member] | Discounted cash flow [Member] | Low [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Price Per Millions of BTU | $ / MMBTU		2.96	1.89
Natural Gas Portfolio [Member] | Discounted cash flow [Member] | High [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Price Per Millions of BTU | $ / MMBTU		7.45	3.42
Natural Gas Portfolio [Member] | Discounted cash flow [Member] | Weighted Average [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Price Per Millions of BTU | $ / MMBTU		5.66	2.47
Natural Gas Portfolio [Member] | Fair Value, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		$ 168,762,000	$ 19,276,000
Derivative Liability		17,105,000	14,352,000
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		72,000	137,000
Derivative Liability		1,756,000	1,272,000
Natural Gas Portfolio [Member] | Fair Value, Recurring [Member] | Parent Company [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets		72,000	137,000
Derivative Liability		$ 1,756,000	$ 1,272,000