Fair Value - Schedule of Activity For Energy Commodity Derivative Assets (Liabilities) Measured At Fair Value Using Significant Unobservable Inputs (Level 3) (Details) - Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (2,628)	$ (2,992)	$ (2,976)	$ (5,262)
Included in regulatory assets/liabilities	(1,046)	(133)	(952)	8,451
Settlements		(9)	254	(6,323)
Ending Balance	(3,674)	(3,134)	(3,674)	(3,134)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(2,628)	(2,992)	(2,976)	(2,774)
Included in regulatory assets/liabilities	(1,046)	(133)	(952)	8,015
Settlements		(9)	254	(8,375)
Ending Balance	$ (3,674)	$ (3,134)	$ (3,674)	(3,134)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				(2,488)
Included in regulatory assets/liabilities				436
Settlements				$ 2,052