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Equity And Earnings Per Share (Narrative) (Details) (USD $)
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3 Months Ended | 6 Months Ended | 12 Months Ended | 36 Months Ended | 86 Months Ended | |||||
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Jun. 30, 2014
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Mar. 31, 2014
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Jun. 30, 2014
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Jun. 30, 2013
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Dec. 31, 2013
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Dec. 31, 2011
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Dec. 31, 2010
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Jun. 30, 2014
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Jun. 30, 2014
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May 03, 2007
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| Equity And Earnings Per Share [Line Items] | ||||||||||
| IBG Inc. ownership % of IBG LLC | 14.10% | 14.10% | 14.10% | 14.10% | 10.00% | |||||
| IBG Holdings ownership % of IBG LLC | 85.90% | 85.90% | 85.90% | 85.90% | 90.00% | |||||
| IBG Holdings Redemption of IBG LLC | 10.00% | |||||||||
| IBG Holdings LLC Ownership Percentage of Class B Common Stock | 100.00% | |||||||||
| Common stock, par value | $ 0.01 | $ 0.01 | $ 0.01 | $ 0.01 | $ 0.01 | |||||
| Preferred stock shares authorized | 10,000 | 10,000 | 10,000 | 10,000 | 10,000 | |||||
| Preferred stock shares issued | 0 | 0 | 0 | 0 | 0 | |||||
| Preferred stock shares outstanding | 0 | 0 | 0 | 0 | 0 | |||||
| Unamortized deferred tax asset arising from equity offerings | $ 283,500,000 | $ 283,500,000 | $ 294,700,000 | $ 283,500,000 | $ 283,500,000 | |||||
| Deferred tax asset arising from equity offerings | 420,400,000 | 420,400,000 | 420,400,000 | 420,400,000 | ||||||
| Percent of Tax Savings Owed to IBG Holdings LLC | 85.00% | |||||||||
| Percentage of tax savings retained by IBG Inc. | 15.00% | |||||||||
| Tax savings owed to IBG Holdings LLC | 357,400,000 | 357,400,000 | 357,400,000 | 357,400,000 | ||||||
| Tax savings retained by IBG Inc. | 63,100,000 | 63,100,000 | 63,100,000 | 63,100,000 | ||||||
| Tax savings paid to IBG Holdings LLC | 15,700,000 | 86,200,000 | ||||||||
| 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 IBG LLC | 5,013,259 | |||||||||
| Cash Redemptions IBG Holdings | 114,000,000 | |||||||||
| Shares Issued | 4,683,415 | 1,983,624 | ||||||||
| Thomas Peterffy and Affiliates Ownership | 87.60% | 87.60% | 87.60% | 87.60% | 84.60% | |||||
| Dividends paid by IBG LLC | 235,800,000 | |||||||||
| Cash dividend paid to IBG, Inc. | 32,300,000 | |||||||||
| Dividends paid to common shareholders | $ 5,700,000 | $ 5,500,000 | $ 11,176,000 | $ 9,745,000 | ||||||
| Declaration Date | Jul. 15, 2014 | |||||||||
| Dividend per share | $ 0.10 | $ 0.10 | $ 0.10 | |||||||
| Payment Date | Sep. 12, 2014 | |||||||||
| Record Date | Aug. 29, 2014 | |||||||||
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Common Class A
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| Equity And Earnings Per Share [Line Items] | ||||||||||
| Shares authorized | 1,000,000,000 | 1,000,000,000 | 1,000,000,000 | 1,000,000,000 | 1,000,000,000 | |||||
| Common stock, shares issued | 57,220,459 | 57,220,459 | 54,788,049 | 57,220,459 | 57,220,459 | |||||
| Common stock, shares outstanding | 57,098,889 | 57,098,889 | 54,664,095 | 57,098,889 | 57,098,889 | |||||
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Common Class B
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| Equity And Earnings Per Share [Line Items] | ||||||||||
| Shares authorized | 100 | 100 | 100 | 100 | 100 | |||||
| Common stock, shares issued | 100 | 100 | 100 | 100 | 100 | |||||
| Common stock, shares outstanding | 100 | 100 | 100 | 100 | 100 | |||||