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Derivative and Hedging Instruments (Details-5)
3 Months Ended 6 Months Ended
Jun. 30, 2019
USD ($)
counterparty
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
counterparty
Jun. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Counterparties in net liability position or default [Abstract]          
Derivative, net liability position of counterparties $ 0   $ 0   $ 0
Number of counterparties in default | counterparty 0   0    
Commodity Derivative Contracts [Member] | Fuel For Electric Generation Purchased Power [Member]          
Realized losses (gains) on income statement [Line Items]          
Realized losses (gains) on income statement $ 299,000 $ (190,000) $ 568,000 $ 184,000  
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]          
Realized losses (gains) on income statement [Line Items]          
Realized losses (gains) on income statement 99,000 22,000 377,000 637,000  
Financial Transmission Rights [Member] | Fuel For Electric Generation Purchased Power [Member]          
Realized losses (gains) on income statement [Line Items]          
Realized losses (gains) on income statement 61,000 (300,000) (74,000) (475,000)  
Financial Transmission Rights [Member] | Cost Of Gas Sold Expense [Member]          
Realized losses (gains) on income statement [Line Items]          
Realized losses (gains) on income statement 0 0 0 0  
Purchased Power Agreement [Member]          
Derivative collateral required to be posted for PPA [Abstract]          
Minimum collateral that may be required to be posted 20,000,000.0   20,000,000.0    
Maximum collateral that may be required to be posted 40,000,000.0   40,000,000.0    
Collateral posted 0   0    
Purchased Power Agreement [Member] | Fuel For Electric Generation Purchased Power [Member]          
Realized losses (gains) on income statement [Line Items]          
Realized losses (gains) on income statement (343,000) 437,000 (752,000) 955,000  
Purchased Power Agreement [Member] | Cost Of Gas Sold Expense [Member]          
Realized losses (gains) on income statement [Line Items]          
Realized losses (gains) on income statement $ 0 $ 0 $ 0 $ 0