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Documentation and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2018
Feb. 25, 2019
Jun. 30, 2018
Entity Registrant Name Interactive Brokers Group, Inc.    
Entity Central Index Key 0001381197    
Document Type 10-K    
Document Period End Date Dec. 31, 2018    
Amendment Flag false    
Fiscal Year Focus 2018    
Fiscal Period Focus FY    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 4,653,486,080
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Common Class A      
Common Stock Shares Outstanding   75,100,952  
Common Class B      
Common Stock Shares Outstanding   100