XML 63 R1.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2019
Feb. 21, 2020
Jun. 30, 2019
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2019    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2019    
Trading Symbol FISI    
Entity Registrant Name FINANCIAL INSTITUTIONS INC    
Entity Central Index Key 0000862831    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity File Number 000-26481    
Entity Tax Identification Number 16-0816610    
Entity Incorporation, State or Country Code NY    
Entity Address, Address Line One 220 LIBERTY STREET    
Entity Address, City or Town WARSAW    
Entity Address, State or Province NY    
Entity Address, Postal Zip Code 14569    
City Area Code 585    
Local Phone Number 786-1100    
Entity Common Stock, Shares Outstanding   16,002,899  
Entity Interactive Data Current Yes    
Document Annual Report true    
Document Transition Report false    
Title of 12(b) Security Common stock, par value $0.01 per share    
Security Exchange Name NASDAQ    
Entity Public Float     $ 457,230,000
Documents Incorporated by Reference

Portions of the registrant’s proxy statement for the 2020 Annual Meeting of Shareholders are incorporated by reference in Part III of this Annual Report on Form 10-K.