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Regulatory Matters (Schedule Of Asset And Liability) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Regulated Asset Liability [Line Items]    
Earning a return, asset $ 258,930  
Not earning a return, asset 284,757  
Pending regulatory treatment, asset 120,462  
Total, asset 664,149 $ 699,828
Earning a return, liability 372,132  
Not earning a return, liability 23,101  
Pending Regulatory Treatment Liability 453,120  
Total, liability 848,353 396,952
Natural Gas Deferrals [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 37,474  
Not earning a return, liability 0  
Pending Regulatory Treatment Liability 0  
Total, liability 37,474 30,820
Power Deferrals [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 29,873  
Not earning a return, liability 0  
Pending Regulatory Treatment Liability 0  
Total, liability 29,873 23,528
Removal Costs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 285,786  
Not earning a return, liability 0  
Pending Regulatory Treatment Liability 0  
Total, liability 285,786 273,983
Deferred Income Tax Charge [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 0  
Not earning a return, liability 18,223  
Pending Regulatory Treatment Liability 442,319  
Total, liability 460,542 28,966
Deferred Derivative Gain (Loss) [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 11,257  
Not earning a return, liability 0  
Pending Regulatory Treatment Liability 7,381  
Total, liability 18,638 21,191
Revenue Subject to Refund [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 0  
Not earning a return, liability 2,350  
Pending Regulatory Treatment Liability 3,420  
Total, liability $ 5,770 10,297
Decoupling [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory liability 1 year  
Earning a return, liability $ 5,816  
Not earning a return, liability 0  
Pending Regulatory Treatment Liability 0  
Total, liability 5,816 2,405
Other Regulatory Assets [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 1,926  
Not earning a return, liability 2,528  
Pending Regulatory Treatment Liability 0  
Total, liability $ 4,454 5,762
Investment In Exchange Power-Net [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 2 years  
Earning a return, asset $ 4,083  
Not earning a return, asset 0  
Pending regulatory treatment, asset 0  
Total, asset 4,083 6,533
Deferred Income Tax Charge [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 90,315  
Not earning a return, asset  
Pending regulatory treatment, asset 0  
Total, asset 90,315 109,853
Pension and Other Postretirement Plans Costs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0  
Not earning a return, asset 209,115  
Pending regulatory treatment, asset 0  
Total, asset 209,115 240,114
Current Regulatory Asset For Utility Derivatives [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0  
Not earning a return, asset 24,991  
Pending regulatory treatment, asset 0  
Total, asset 24,991 11,365
Unamortized Debt Repurchase Costs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 11,880  
Not earning a return, asset 0  
Pending regulatory treatment, asset 0  
Total, asset $ 11,880 13,700
Regulatory Asset For Settlement With Coeur d'Alene Tribe [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 42 years  
Earning a return, asset $ 43,954  
Not earning a return, asset 0  
Pending regulatory treatment, asset 0  
Total, asset 43,954 45,265
Demand Side Management Programs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0  
Not earning a return, asset 24,620  
Pending regulatory treatment, asset 0  
Total, asset $ 24,620 15,700
Decoupling [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 1 year  
Earning a return, asset $ 22,359  
Not earning a return, asset 0  
Pending regulatory treatment, asset 0  
Total, asset 22,359 43,126
Asset Impairment for Regulatory Action [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 24,330  
Not earning a return, asset 0  
Pending regulatory treatment, asset 0  
Total, asset 24,330 19,100
Deferred Derivative Gain (Loss) [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 53,797  
Not earning a return, asset 0  
Pending regulatory treatment, asset 115,907  
Total, asset 169,704 161,508
Non Current Regulatory Asset For Utility Derivatives [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0  
Not earning a return, asset 18,967  
Pending regulatory treatment, asset 0  
Total, asset 18,967 16,919
Other Regulatory Assets [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 8,212  
Not earning a return, asset 7,064  
Pending regulatory treatment, asset 4,555  
Total, asset $ 19,831 $ 16,645
Avista Utilities [Member]    
Regulated Asset Liability [Line Items]    
Tax Cuts and Jobs Act Period to Return Plant Related Excess Deferred Income Taxes 36 years  
Alaska Electric Light & Power [Member]    
Regulated Asset Liability [Line Items]    
Tax Cuts and Jobs Act Period to Return Plant Related Excess Deferred Income Taxes 40 years