v2.4.0.6
Equity and Earnings Per Share Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 12 Months Ended 36 Months Ended 71 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Mar. 31, 2013
Dec. 31, 2012
May 03, 2007
Equity and earnings per share              
IBG Inc. ownership % of IBG LLC 11.90%       11.90%   10.00%
IBG Holdings ownership % of IBG LLC 88.10%       88.10%   90.00%
IBG Holdings Redemption of IBG LLC             10.00%
IBG Holdings LLC Owernship Percentage of Class B Common Stock             100.00%
Preferred stock shares authorized 10,000       10,000 10,000  
Preferred stock shares issued 0       0 0  
Preferred stock shares outstanding 0       0 0  
Amortization period DTA (years) 15       15    
Deferred tax asset from common stock offerings $ 276,601       $ 276,601 $ 281,615  
Percent of Tax Savings Owed to IBG Holdings LLC 85.00%       85.00%    
Percentage of tax savings retained by IBG Inc. 15.00%       15.00%    
Deferred tax asset arising from Common Stock offerings 387,069       387,069    
Tax savings owed to IBG Holdings LLC 329,009       329,009    
Tax savings retained by IBG Inc. 58,060       58,060    
Tax savings paid to IBG Holdings LLC         70,400    
Exchange Agreement Future Redemption Schedule         12.5% annually for seven (7) years and 2.5% in the eighth year.    
Shares reserved for future issuance             360,000,000
Shares redeemed by IBG Holdings from from IBG LLC       5,013,259      
Cash Redemptions IBG Holdings       114,000      
Shares Issued     1,983,624        
Thomas Peterffy and Affiliates Ownership 86.30%       86.30%   84.60%
Dividends paid by IBG LLC 39,900            
Cash dividend paid to IBG, Inc. 4,700            
Dividend per share $ 0.1            
Dividends paid to common shareholders $ 4,750 $ 4,557          
Declaration Date Apr. 16, 2013            
Record Date May 31, 2013            
Payment Date Jun. 14, 2013            
Common Class A
              
Equity and earnings per share              
Common stock, par value $ 0.01       $ 0.01 $ 0.01  
Shares authorized 1,000,000,000       1,000,000,000 1,000,000,000  
Common stock, shares issued 47,801,449       47,801,449 47,797,844  
Common stock, shares outstanding 47,505,086       47,505,086 47,499,739  
Common Class B
              
Equity and earnings per share              
Common stock, par value $ 0.01       $ 0.01 $ 0.01  
Shares authorized 100       100 100  
Common stock, shares issued 100       100 100  
Common stock, shares outstanding 100       100 100