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Document And Entity Information
 12 Months Ended
Dec. 31, 2021
shares
Dec. 31, 2021
shares
Document Information [Line Items]    
Entity Registrant Name Colliers International Group Inc.  
Document, Type 40-F  
Document, Annual Report true  
Document, Period End Date Dec. 31, 2021  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus FY  
Document Fiscal Year Focus 2021  
Entity, File Number 001-36898  
Entity, Incorporation, State or Country Code A6  
Entity, Address, Address Line One 1140 Bay Street, Suite 4000  
Entity, Address, City or Town Toronto  
Entity, Address, State or Province ON  
Entity, Address, Country CA  
Entity, Address, Postal Zip Code M5S 2B4  
City Area Code 416  
Local Phone Number 960-9500  
Title of 12(b) Security Subordinate Voting Shares  
Trading Symbol CIGI  
Security Exchange Name NASDAQ  
Entity, Current Reporting Status Yes  
Entity, Interactive Data, Current Yes  
Entity, Emerging Growth Company false  
ICFR Auditor Attestation Flag true  
Amendment Flag false  
Entity Central Index Key 0000913353  
Document Registration Statement false  
Annual Information Form true  
Audited Annual Financial Statements true  
Auditor Firm ID 271  
Auditor Name PricewaterhouseCoopers LLP PricewaterhouseCoopers LLP
Auditor Location Toronto, Canada Toronto, Canada
Business Contact [Member]    
Document Information [Line Items]    
Entity, Address, Address Line One 126 Prospect Street  
Entity, Address, City or Town Cambridge  
Entity, Address, State or Province MA  
Entity, Address, Postal Zip Code 02139  
City Area Code 617  
Local Phone Number 868-5000  
Contact Personnel Name Mr. Santino Ferrante, Ferrante & Associates  
SubordinateVotingShares Custom [Member]    
Document Information [Line Items]    
Entity, Common Stock Shares, Outstanding 42,729,050 42,729,050
MultipleVotingShares Custom [Member]    
Document Information [Line Items]    
Entity, Common Stock Shares, Outstanding 1,325,694 1,325,694