Document And Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 01, 2019
Document And Entity Information [Abstract]    
Entity Registrant Name AVISTA CORPORATION  
Amendment Flag false  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Title of 12(b) Security Common Stock  
Entity Information, Former Legal or Registered Name None  
City Area Code 509  
Entity Incorporation, State or Country Code WA  
Document Transition Report false  
Document Quarterly Report true  
Document Type 10-Q  
Document Period End Date Sep. 30, 2019  
Entity File Number 1-3701  
Entity Tax Identification Number 91-0462470  
Entity Address, Address Line One 1411 East Mission Avenue  
Entity Address, City or Town Spokane  
Entity Address, State or Province WA  
Entity Address, Postal Zip Code 99202-2600  
Local Phone Number 489-0500  
Trading Symbol AVA  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Emerging Growth Company false  
Entity Shell Company false  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Entity Central Index Key 0000104918  
Current Fiscal Year End Date --12-31  
Entity Common Stock, Shares Outstanding   66,709,945