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Accounting For Income Taxes (Narrative) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Components of Income Tax Expense (Benefit) [Line Items]        
Regulatory liability for excess deferred income taxes   $ 442,319 $ 0  
Tax Cuts and Jobs Act Excess Deferred Income Taxes   339,900    
Tax Cuts and Jobs Act Income Tax Gross Up of Excess Deferred Income Taxes   102,400    
TCJA Change in Income Tax Expense (Benefit)   $ 10,200    
Federal statutory tax rate 21.00% 35.00% 35.00% 35.00%
Avista Utilities [Member]        
Components of Income Tax Expense (Benefit) [Line Items]        
Tax Cuts and Jobs Act Period to Return Plant Related Excess Deferred Income Taxes   36 years    
TCJA Change in Income Tax Expense (Benefit)   $ 7,500    
Alaska Electric Light & Power [Member]        
Components of Income Tax Expense (Benefit) [Line Items]        
Tax Cuts and Jobs Act Period to Return Plant Related Excess Deferred Income Taxes   40 years    
Corporate and Other [Member]        
Components of Income Tax Expense (Benefit) [Line Items]        
TCJA Change in Income Tax Expense (Benefit)   $ 2,700