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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (2,253)	$ (2,716)	$ (2,976)	$ (5,262)
Included in regulatory assets/liabilities	(391)	625	94	8,584
Settlements	16	(901)	254	(6,314)
Ending Balance	(2,628)	(2,992)	(2,628)	(2,992)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(2,253)	(2,104)	(2,976)	(2,774)
Included in regulatory assets/liabilities	(391)	(829)	94	8,148
Settlements	16	(59)	254	(8,366)
Ending Balance	$ (2,628)	(2,992)	$ (2,628)	(2,992)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		(612)		(2,488)
Included in regulatory assets/liabilities		1,454		436
Settlements		$ (842)		$ 2,052