Note 1 - Description of the Business (Details Textual)	Dec. 31, 2018
Number of Countries in which Entity Operates	35
Number of Geographic Regions in which Entity Operates	4
Colliers and Its Affiliates and Franchisees [Member]
Number of Countries in which Entity Operates	68

The number of geographic regions in which the entity operates as of the balance sheet date.

No definition available.

Name:	cigi_NumberOfGeographicRegionsInWhichEntityOperates
Namespace Prefix:	cigi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant