Interactive Brokers (IBKR) 10-Q 10 Nov 14 2014 Q3 Quarterly report Financial data

Documentation_and_Entity_Infor

Documentation and Entity Information	9 Months Ended
	Sep. 30, 2014	Nov. 10, 2014	Nov. 10, 2014
		Common Class A	Common Class B
Entity Registrant Name	'Interactive Brokers Group, Inc.	'	'
Entity Central Index Key	'0001381197	'	'
Document Type	'10-Q	'	'
Document Period End Date	30-Sep-14	'	'
Amendment Flag	'false	'	'
Fiscal Year Focus	'2014	'	'
Fiscal Period Focus	'Q3	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Common Stock Shares Outstanding	'	58,463,160	100

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Financial Condition (Unaudited) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets	'	'
Cash and cash equivalents	$1,010,759	$1,213,241
Cash and securities - segregated for regulatory purposes	15,291,298	13,991,711
Securities borrowed	2,955,064	2,751,501
Securities purchased under agreements to resell	273,536	386,316
Financial instruments owned, at fair value:	'	'
Financial instruments owned	2,236,853	3,285,313
Financial instruments owned and pledged as collateral	1,159,323	1,163,531
Total financial instruments owned, at fair value	3,396,176	4,448,844
Receivables:	'	'
Customers, less allowance for doubtful accounts of $8,153 and $67,999 at September 30, 2014 and December 31, 2013	17,261,440	13,596,650
Brokers, dealers and clearing organizations	885,333	858,189
Receivable from affiliate	8	55
Interest	46,325	26,489
Total receivables	18,193,106	14,481,383
Other assets	488,267	597,704
Total assets	41,608,206	37,870,700
Liabilities and equity	'	'
Financial instruments sold, but not yet purchased, at fair value	2,649,664	3,153,673
Securities loaned	3,116,395	2,563,653
Short-term borrowings	59,362	24,635
Payables:	'	'
Customers	29,966,079	26,319,420
Brokers, dealers and clearing organizations	238,670	330,956
Payable to affiliate	271,467	287,242
Accounts payable, accrued expenses and other liabilities	108,267	96,026
Interest	5,676	2,969
Total payables	30,590,159	27,036,613
Total liabilities	36,415,580	32,778,574
Stockholders' equity:	'	'
Additional paid-in capital	615,943	583,312
Retained earnings	119,423	98,868
Accumulated other comprehensive income, net of income taxes of $868 and $936 at September 30, 2014 and December 31, 2013	18,089	27,028
Treasury stock, at cost,142,467 and 123,954 shares at September 30, 2014 and December 31, 2013	-3,167	-2,492
Total stockholders' equity	750,860	707,264
Noncontrolling interests	4,441,766	4,384,862
Total equity	5,192,626	5,092,126
Total liabilities and equity	41,608,206	37,870,700
Common Class A	'	'
Stockholders' equity:	'	'
Common stock	572	548
Common Class B	'	'
Stockholders' equity:	'	'
Common stock	$0	$0

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Financial Condition (Unaudited) (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Allowance for doubtful accounts	$8,153	$67,999
Common stock, par value	$0.01	$0.01
Accumulated Other Comprehensive Income, Tax	$868	$936
Treasury stock shares	142,467	123,954
Common Class A	'	'
Shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	57,247,149	54,788,049
Common stock, shares outstanding	57,104,682	54,664,095
Common Class B	'	'
Shares authorized	100	100
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues:	'	'	'	'
Trading gains (losses)	($75,693)	$123,286	$135,839	$201,386
Commissions and execution fees	132,539	120,331	393,531	377,961
Interest income	122,371	74,000	303,281	220,572
Other income	15,887	20,826	52,888	64,999
Total revenues	195,104	338,443	885,539	864,918
Interest expense	24,130	12,191	50,358	38,636
Total net revenues	170,974	326,252	835,181	826,282
Non-interest expenses:	'	'	'	'
Execution and clearing	52,152	56,016	157,996	180,283
Employee compensation and benefits	49,408	44,242	156,483	148,578
Occupancy, depreciation and amortization	9,393	9,387	28,905	28,705
Communications	5,975	6,125	18,162	17,281
General and administrative	14,665	14,100	41,901	38,904
Total non-interest expenses	131,593	129,870	403,447	413,751
Income before income taxes	39,381	196,382	431,734	412,531
Income tax expense	7,691	10,414	38,092	31,239
Net income	31,690	185,968	393,642	381,292
Less net income attributable to noncontrolling interests	28,499	169,521	356,201	347,910
Net income available for common stockholders	3,191	16,447	37,441	33,382
Earnings per share:	'	'	'	'
Basic	$0.06	$0.33	$0.67	$0.68
Diluted	$0.05	$0.32	$0.65	$0.67
Weighted average common shares outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	57,099,052	49,966,050	55,956,615	48,807,321
Weighted Average Number of Shares Outstanding, Diluted	58,220,070	50,988,214	57,196,113	49,981,664
Comprehensive income:	'	'	'	'
Net income available for common stockholders	3,191	16,447	37,441	33,382
Other comprehensive income:	'	'	'	'
Cumulative translation adjustment, before income taxes	-11,037	3,691	-9,007	-4,051
Income taxes related to items of other comprehensive income	-252	61	-68	-335
Other comprehensive income (loss), net of tax	-10,785	3,630	-8,939	-3,716
Comprehensive income (loss) available for common stockholders	-7,594	20,077	28,502	29,666
Comprehensive income attributable to noncontrolling interests:	'	'	'	'
Net income attributable to noncontrolling interests	28,499	169,521	356,201	347,910
Other comprehensive income (loss) - cumulative translation adjustment	-67,154	26,013	-54,483	-29,602
Comprehensive income (loss) attributable to noncontrolling interests	($38,655)	$195,534	$301,718	$318,308

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:	'	'
Net income	$393,642	$381,292
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Deferred income taxes	14,844	11,164
Depreciation and amortization	14,075	13,914
Employee stock plan compensation	31,467	28,086
Losses (gains) on other investments, net	8,908	-2,728
Bad debt expense	2,504	2,472
Change in operating assets and liabilities:	'	'
Increase in cash and securities - segregated for regulatory purposes	-1,301,260	-512,361
Increase in securities borrowed	-203,563	-530,097
Decrease (increase) in securities purchased under agreements to resell	112,780	-58,870
Decrease in financial instruments owned, at fair value	1,052,608	119,463
Increase in receivables from customers	-3,667,294	-2,876,534
(Increase) decrease in other receivables	-46,933	352,287
Decrease in other assets	6,095	23,857
Decrease in financial instruments sold, but not yet purchased, at fair value	-504,009	-692,968
Increase in securities loaned	552,742	353,734
Increase in payable to customers	3,646,659	3,387,371
Decrease in other payables	-74,050	-127,594
Net cash provided by (used in) operating activities	39,215	-127,512
Cash flows from investing activities:	'	'
Purchases of other investments	-420,928	-189,934
Proceeds from sales of other investments	497,610	202,245
Distributions received from and redemptions of equity investments	1,074	11,054
Purchase of property and equipment	-13,961	-12,006
Net cash provided by investing activities	63,795	11,359
Cash flows from financing activities:	'	'
Dividends paid to stockholders	-16,886	-14,742
Distributions to noncontrolling interests	-244,159	-107,698
Payments made under the Tax Receivable Agreement	-15,752	'
Increase (decrease) in short-term borrowings, net	34,727	-107,841
Net cash used in financing activities	-242,070	-230,281
Effect of exchange rate changes on cash and cash equivalents	-63,422	-33,317
Net decrease in cash and cash equivalents	-202,482	-379,751
Cash and cash equivalents at beginning of period	1,213,241	1,380,599
Cash and cash equivalents at end of period	1,010,759	1,000,848
Supplemental disclosures of cash flow information:	'	'
Cash paid for interest	47,651	40,661
Cash paid for taxes	26,503	45,243
Non-cash financing activities:	'	'
Adjustments to additional paid-in capital for changes in proportionate ownership in IBG LLC	28,221	20,463
Adjustments to noncontrolling interests for changes in proportionate ownership in IBG LLC	($28,221)	($20,463)

Condensed_Consolidated_Stateme4

Condensed Consolidated Statements of Changes in Equity (Unaudited) (USD $)	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Total Stockholders' Equity [Member]	Noncontrolling Interests [Member]	Total
In Thousands, except Share data
Balance at Dec. 31, 2012	$478	$493,912	($7,718)	$82,072	$29,754	$598,498	$4,214,649	$4,813,147
Common stock, shares issued at Dec. 31, 2012	47,797,844	'	'	'	'	'	'	'
Common stock distributed pursuant to stock plans	23	-23	5,200	'	'	5,200	'	5,200
Common Stock distributed pursuant to stock plans (in shares)	2,298,718	'	'	'	'	'	'	'
Compensation for stock grants vesting in the future	'	3,513	'	'	'	3,513	25,488	29,001
Dividends paid to stockholders	'	'	'	-14,742	'	-14,742	'	-14,742
Distributions from IBG LLC to noncontrolling interests	'	'	'	'	'	'	-107,698	-107,698
Adjustments for changes in proportionate ownership in IBG LLC	'	20,463	'	'	'	20,463	-20,463	'
Comprehensive Income	'	'	'	33,382	-3,716	29,666	318,308	347,974
Balance at Sep. 30, 2013	501	517,865	-2,518	100,712	26,038	642,598	4,430,284	5,072,882
Common stock, shares issued at Sep. 30, 2013	50,096,562	'	'	'	'	'	'	'
Balance at Dec. 31, 2013	548	583,312	-2,492	98,868	27,028	707,264	4,384,862	5,092,126
Common stock, shares issued at Dec. 31, 2013	54,788,049	'	'	'	'	'	'	'
Common stock distributed pursuant to stock plans	24	-24	75	'	'	75	'	75
Common Stock distributed pursuant to stock plans (in shares)	2,438,091	'	'	'	'	'	'	'
Compensation for stock grants vesting in the future	'	4,359	'	'	'	4,359	27,108	31,467
Stock Incentive Plan Adjustment	'	75	-750	'	'	-675	458	-217
Stock Incentive Plan Adjustment (in shares)	21,109	'	'	'	'	'	'	'
Dividends paid to stockholders	'	'	'	-16,886	'	-16,886	'	-16,886
Distributions from IBG LLC to noncontrolling interests	'	'	'	'	'	'	-244,159	-244,159
Adjustments for changes in proportionate ownership in IBG LLC	'	28,221	'	'	'	28,221	-28,221	'
Comprehensive Income	'	'	'	37,441	-8,939	28,502	301,718	330,220
Balance at Sep. 30, 2014	$572	$615,943	($3,167)	$119,423	$18,089	$750,860	$4,441,766	$5,192,626
Common stock, shares issued at Sep. 30, 2014	57,247,249	'	'	'	'	'	'	'

Organization_And_Nature_Of_Bus

Organization And Nature Of Business	9 Months Ended
	Sep. 30, 2014
Organization And Nature Of Business [Abstract]	'
Organization And Nature Of Business	'
	1. Organization and Nature of Business
	Interactive Brokers Group, Inc. (“IBG, Inc.”) is a Delaware holding company whose primary asset is its ownership of approximately 14.1% of the membership interests of IBG LLC, which, in turn, owns operating subsidiaries (collectively “IBG LLC”). IBG, Inc. together with IBG LLC and its consolidated subsidiaries (collectively, “the Company”), is an automated global electronic broker and market maker specializing in executing and clearing trades in securities, futures, foreign exchange instruments, bonds and mutual funds on more than 100 electronic exchanges and trading venues around the world and offering custody, prime brokerage, securities and margin lending services to customers. In the United States of America (“U.S.”), the Company’s business is conducted from its headquarters in Greenwich, Connecticut, from Chicago, Illinois and from Jersey City, New Jersey. Abroad, business is conducted through offices located in Canada, England, Switzerland, Liechtenstein, China (Hong Kong and Shanghai), Japan, India, and Australia. At September 30, 2014, the Company had 937 employees worldwide.
	IBG LLC is a Connecticut limited liability company that conducts its business through its operating subsidiaries (collectively called the “Operating Companies”):  Interactive Brokers LLC (“IB LLC”) and its subsidiary, Interactive Brokers Corp. (“IB Corp”); Interactive Brokers Canada Inc. (“IBC”); Interactive Brokers (U.K.) Limited and its subsidiary, Interactive Brokers (U.K.) Nominee Limited (collectively  “IBUK”); Interactive Brokers Securities Japan, Inc. (“IBSJ”); Interactive Brokers (India) Private Limited (“IBI”);  Timber Hill LLC (“TH LLC”); Timber Hill Europe AG and its subsidiary, Timber Hill (Liechtenstein) AG (collectively “THE”); Timber Hill Securities Hong Kong Limited (“THSHK”); Timber Hill Australia Pty Limited (“THA”); Timber Hill Canada Company (“THC”); Interactive Brokers Financial Products S.A. (“IBFP”); Interactive Brokers Hungary KFT (“IBH”); IB Exchange Corp. (“IBEC”); Interactive Brokers Software Services Estonia OU (“IBEST”) and Interactive Brokers Software Services Russia (“IBRUS”).
	The Company operates in two business segments: electronic brokerage and market making. The Company conducts its electronic brokerage business through certain Interactive Brokers subsidiaries, which provide electronic execution and clearing services to customers worldwide. The Company conducts its market making business principally through its Timber Hill subsidiaries on the world’s leading exchanges and market centers, primarily in exchange‑traded equities, equity options and equity‑index options and futures.
	Certain of the Operating Companies are members of various securities and commodities exchanges in North America, Europe and the Asia/Pacific region and are subject to regulatory capital and other requirements (see Note 13). IB LLC, IBUK, IBC, IBI and IBSJ carry securities accounts for customers or perform custodial functions relating to customer securities.

Significant_Accounting_Policie

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2014
Significant Accounting Policies [Abstract]	'
Significant Accounting Policies	'
	2. Significant Accounting Policies
	Basis of Presentation
	These condensed consolidated financial statements are presented in U.S. dollars and have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding financial reporting with respect to Form 10-Q.
	These condensed consolidated financial statements are unaudited and should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s 2013 Annual Report on Form 10-K for the year ended December 31, 2013, which was filed with the SEC on March 3, 2014. The condensed consolidated financial information as of December 31, 2013 has been derived from the audited consolidated financial statements not included herein.
	These unaudited condensed consolidated financial statements include the accounts of the Company and its consolidated subsidiaries and reflect all adjustments of a normal and recurring nature that are, in the opinion of management, necessary for the fair  presentation of the results for the interim periods presented.  The operating results for interim periods are not necessarily indicative of the operating results for the entire year.
	Principles of Consolidation, including Noncontrolling Interests
	These condensed consolidated financial statements include the accounts of IBG, Inc. and its majority and wholly owned subsidiaries.  As sole managing member of IBG LLC, IBG, Inc. exerts control over the IBG LLC’s operations. In accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810, “Consolidation”, the Company consolidates IBG LLC’s financial statements and records the interests in IBG LLC that it does not own as noncontrolling interests.
	The Company’s policy is to consolidate all other entities in which it owns more than 50% unless it does not have control. All inter‑company balances and transactions have been eliminated.
	Use of Estimates
	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in these condensed consolidated financial statements and accompanying notes. These estimates and assumptions are based on judgment and the best available information at the time. Therefore, actual results could differ materially from those estimates. Such estimates include the allowance for doubtful accounts, valuation of certain investments, compensation accruals, current and deferred income taxes, and estimated contingency reserves.
	Fair Value
	Substantially all of the Company’s assets and liabilities, including financial instruments are carried at fair value based on published market prices and are marked to market, or are assets and liabilities which are short‑term in nature and are carried at amounts that approximate fair value.
	The Company applies the fair value hierarchy in accordance with FASB ASC Topic 820, “Fair Value Measurement” (“ASC Topic 820”), to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets and liabilities and the lowest priority to unobservable inputs. The three levels of the fair value hierarchy are:
	Level 1	Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.
	Level 2	Quoted prices in markets that are not considered to be active or financial instruments for which all significant inputs are observable, either directly or indirectly.
	Level 3	Prices or valuations that require inputs that are both significant to fair value measurement and unobservable.
	Financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are generally classified as Level 1 of the fair value hierarchy. The Company’s Level 1 financial instruments, which are valued using quoted market prices as published by exchanges and clearing houses or otherwise broadly distributed in active markets, include active listed stocks, options, warrants and discount certificates, U.S. and foreign government securities and corporate and municipal bonds.  The Company does not adjust quoted prices for Level 1 financial instruments, even in the event that the Company may hold a large position whereby a purchase or sale could reasonably impact quoted prices.
	Currency forward contracts are valued using broadly distributed bank and broker prices, and are classified as Level 2 of the fair value hierarchy as such instruments are not exchange‑traded. Other securities that are not traded in active markets are also classified in Level 2 of the fair value hierarchy. Level 3 financial instruments are comprised of securities that have been delisted or otherwise are no longer tradable and have been valued by the Company based on internal estimates.
	Other fair value investments, included in other assets in the condensed consolidated statements of financial condition, are comprised of listed stocks, options, and corporate and municipal bonds that the Company does not carry in its market making business.  These investments are generally reported as Level 2 of the fair value hierarchy, except for unrestricted listed securities, which are classified as Level 1 of the fair value hierarchy, and delisted securities which are classified as Level 3 of the fair value hierarchy.  Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities in the condensed consolidated statements of financial condition, are comprised of unrestricted listed securities which are classified as Level 1 of the fair value hierarchy.
	Earnings Per Share
	Earnings per share (“EPS”) are computed in accordance with FASB ASC Topic 260,  “Earnings per Share.”   Basic EPS is computed by dividing the net income available for common stockholders by the weighted average number of shares outstanding for that period. Diluted EPS is calculated by dividing the net income available for common stockholders by the diluted weighted average shares outstanding for that period. Diluted EPS includes the determinants of the basic EPS and, in addition, reflects the dilutive effect of shares of common stock estimated to be distributed in the future under the Company’s stock-based compensation plans, with no adjustments to net income available for common stockholders for dilutive potential common shares.
	Stock‑Based Compensation
	The Company follows FASB ASC Topic 718, “Compensation - Stock Compensation” (“ASC Topic 718”), to account for its stock‑based compensation plans. ASC Topic 718 requires all share‑based payments to employees to be recognized in the condensed consolidated financial statements using a fair value‑based method. Grants, which are denominated in U.S. dollars, are communicated to employees in the year of grant, thereby establishing the fair value of each grant. The fair value of awards granted to employees are generally expensed as follows: 50% in the year of grant in recognition of plan forfeiture provisions (as described below) and the remaining 50% over the related vesting period utilizing the “graded vesting” method permitted under ASC Topic 718. In the case of “retirement eligible” employees (those employees older than 59), 100% of awards are expensed when granted.
	Awards granted under stock‑based compensation plans are subject to forfeiture in the event an employee ceases employment with the Company. The plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted.
	Cash and Cash Equivalents
	The Company considers all highly liquid investments, with maturities of three months or less, that are not segregated and deposited for regulatory purposes or to meet margin requirements at clearing houses to be cash equivalents.
	Cash and Securities - Segregated for Regulatory Purposes
	As a result of customer activities, certain Operating Companies are obligated by rules mandated by their primary regulators to segregate or set aside cash or qualified securities to satisfy such regulations, which regulations have been promulgated to protect customer assets. Securities segregated for regulatory purposes consisted of U.S. Treasury Bills of $4.58 billion and $1.30 billion at September 30, 2014 and December 31, 2013, respectively, and securities purchased under agreements to resell in the amount of $5.25 billion and $6.73 billion as of September 30, 2014 and December 31, 2013, respectively, which amounts approximate fair value.
	Securities Borrowed and Securities Loaned
	Securities borrowed and securities loaned are recorded at the amount of the cash collateral advanced or received. Securities borrowed transactions require the Company to provide counterparties with collateral, which may be in the form of cash, letters of credit or other securities. With respect to securities loaned, the Company receives collateral, which may be in the form of cash or other securities in an amount generally in excess of the fair value of the securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as permitted contractually. The Company does not net, in the condensed consolidated statements of financial condition, securities borrowed and securities loaned entered into with the same counterparty.
	Securities lending fees received and paid by the Company are included in interest income or interest expense, respectively, in the condensed consolidated statements of comprehensive income.
	Securities Purchased Under Agreements to Resell
	Securities purchased under agreements to resell, which are reported as collateralized financing transactions, are recorded at contract value, plus accrued interest, which approximates fair value. To ensure that the fair value of the underlying collateral remains sufficient, the collateral is valued daily with additional collateral obtained or excess collateral returned, as permitted under contractual provisions. The Company does not net, in the condensed consolidated statements of financial condition, securities purchased under agreements to resell transactions and securities sold under agreements to repurchase transactions entered into with the same counterparty.
	Financial Instruments Owned and Financial Instruments Sold, But Not Yet Purchased, at Fair Value
	Financial instrument transactions are accounted for on a trade date basis. Financial instruments owned and financial instruments sold, but not yet purchased are stated at fair value based upon quoted market prices. All firm‑owned financial instruments pledged to counterparties where the counterparty has the right, by contract or custom, to sell or repledge the financial instruments are reported as financial instruments owned and pledged as collateral in the condensed consolidated statements of financial condition.
	The Company also enters into currency forward contracts. These transactions, which are also accounted for on a trade date basis, are agreements to exchange a fixed amount of one currency for a specified amount of a second currency at completion of the currency forward contract term. Unrealized mark‑to‑market gains and losses on currency forward contracts are included in financial instruments owned, at fair value or financial instruments sold, but not yet purchased, at fair value in the condensed consolidated statements of financial condition.
	Customer Receivables and Payables
	Customer securities transactions are recorded on a settlement date basis and customer commodities transactions are recorded on a trade date basis. Receivables from and payables to customers include amounts due on cash and margin transactions, including futures contracts transacted on behalf of customers. Securities owned by customers, including those that collateralize margin loans or other similar transactions, are not reported in the condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are expensed and included in general and administrative expense in the condensed consolidated statements of comprehensive income.
	Receivables from and Payables to Brokers, Dealers and Clearing Organizations
	Receivables and payables to brokers, dealers and clearing organizations include net receivables and payables from unsettled trades, including amounts related to futures and options on futures contracts executed on behalf of customers, amounts receivable for securities not delivered by the Company to the purchaser by the settlement date (“fails to deliver”) and cash margin deposits. Payables to brokers, dealers and clearing organizations also include amounts payable for securities not received by the Company from a seller by the settlement date (“fails to receive”).
	Investments
	The Company makes certain strategic investments related to its business and accounts for these investments under the cost method of accounting or under the equity method of accounting as required under FASB ASC Topic 323, “Investments—Equity Method and Joint Ventures.”   Investments accounted for under the equity method, including where the investee is a limited partnership or limited liability company, are recorded at the fair value amount of the Company’s initial investment and are adjusted each period for the Company’s share of the investee’s income or loss. The Company’s share of the income or losses from equity method investments is included in other income in the condensed consolidated statements of comprehensive income. The recorded amounts of the Company’s equity method investments, $34.7 million at September 30, 2014 ($27.5 million at December 31, 2013), which are included in other assets in the condensed consolidated statements of financial condition, increase or decrease accordingly. Contributions paid to and distributions received from equity method investees are recorded as additions or reductions, respectively, to the respective investment balance.
	The Company also holds exchange memberships and investments in equity securities of certain exchanges as required to qualify as a clearing member, and strategic investments in corporate stock that do not qualify for equity method accounting. Such investments, $30.1 million at September 30, 2014 ($27.6 million at December 31, 2013), are recorded at cost or, if an other‑than‑temporary impairment in value has occurred, at a value that reflects management’s estimate of the impairment, and are also included in other assets in the condensed consolidated statements of financial condition. Dividends received from cost basis investments are included in other income in the condensed consolidated statements of comprehensive income when such dividends are received.
	A judgmental aspect of accounting for investments is evaluating whether an other‑than‑temporary decline in the value of an investment has occurred. The evaluation of an other‑than‑temporary impairment is dependent on specific quantitative and qualitative factors and circumstances surrounding an investment, including recurring operating losses, credit defaults and subsequent rounds of financing.  The Company’s equity investments do not have readily determinable market values. All investments are reviewed for changes in circumstances or occurrence of events that suggest the Company’s investment may not be recoverable. If an unrealized loss on any investment is considered to be other‑than‑temporary, the loss is recognized in the period the determination is made
	The Company also has certain investments (which are not considered core business activities) that are accounted for at fair value (see Note 6) and included in other assets in the condensed consolidated statements of financial condition.  Gains and losses related to these investments are included in other income in the condensed consolidated statements of comprehensive income.
	Property and Equipment
	Property and equipment, which is included in other assets in the condensed consolidated statements of financial condition, consists of purchased technology hardware and software, internally developed software, leasehold improvements and office furniture and equipment. Property and equipment are recorded at historical cost, less accumulated depreciation and amortization. Additions and improvements that extend the lives of assets are capitalized, while expenditures for repairs and maintenance are expensed as incurred. Depreciation and amortization are computed using the straight‑line method. Equipment is depreciated over the estimated useful lives of the assets, while leasehold improvements are amortized over the lesser of the estimated economic useful life of the asset or the term of the lease. Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years.
	Comprehensive Income and Foreign Currency Translation
	The Company’s operating results are reported in the condensed consolidated statements of comprehensive income pursuant to FASB Accounting Standards Update 2011‑05, “Comprehensive Income”.
	Comprehensive income consists of two components: net income and other comprehensive income (“OCI”). OCI is comprised of revenues, expenses, gains and losses that are reported in the comprehensive income section of the statements of comprehensive income, but are excluded from reported net income. The Company’s OCI is comprised of foreign currency translation adjustments, net of related income taxes, where applicable. In general, the practice and intention of the Company is to reinvest the earnings of its non‑U.S. subsidiaries in those operations.
	The Company’s non‑U.S. domiciled subsidiaries have a functional currency that is other than the U.S. dollar. Such subsidiaries’ assets and liabilities are translated into U.S. dollars at period‑end exchange rates, and revenues and expenses are translated at average exchange rates prevailing during the period. Adjustments that result from translating amounts from a subsidiary’s functional currency to the U.S. dollar are reported net of tax, where applicable, in accumulated OCI in the condensed consolidated statements of financial condition.
	Revenue Recognition
	—Trading Gains (Losses)
	Trading gains and losses are recorded on trade date and are reported on a net basis. Trading gains and losses are comprised of changes in the fair value of financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value (i.e., unrealized gains and losses) and realized gains and losses. Included in trading gains (losses) are net gains and losses on stocks, U.S. and foreign government securities, corporate and municipal bonds, options, futures, foreign exchange and other derivative instruments. Dividends are integral to the valuation of stocks and interest is integral to the valuation of fixed income instruments. Accordingly, both dividends and interest income and expense attributable to financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are reported on a net basis included in trading gains (losses) in the condensed consolidated statements of comprehensive income.
	—Commissions and Execution Fees
	Commissions charged for executing and clearing customer transactions are recorded on a trade date basis and are reported as commissions and execution fees and the related expenses are reported as execution and clearing expenses in the condensed consolidated statements of comprehensive income.
	—Interest Income and Expense
	The Company earns interest income and incurs interest expense primarily in connection with its electronic brokerage customer business and its securities lending activities, which are recorded on the accrual basis and are included in interest income and interest expense, respectively, in the condensed consolidated statements of comprehensive income.
	—Foreign Currency Transaction Gains and Losses
	Foreign currency transaction gains and losses from market making are included in trading gains (losses) in the condensed consolidated statements of comprehensive income. Electronic brokerage foreign currency transaction gains and losses are included in interest income (if arising from currency swap transactions) or other income in the condensed consolidated statements of comprehensive income.
	Income Taxes
	The Company accounts for income taxes in accordance with FASB ASC Topic740, “Income Taxes” (“ASC Topic 740”). The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits are based on enacted tax laws (see Note 10) and reflect management’s best assessment of estimated future taxes to be paid. The Company is subject to income taxes in both the U.S. and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates.
	The Company recognizes interest related to income tax matters as interest income or expense and penalties related to income tax matters as income tax expense.
Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statements recognition of the underlying assets and liabilities. In evaluating the ability to recover deferred tax assets within the jurisdictions from which they arise, the Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax‑planning strategies, and results of recent operations. In projecting future taxable income, historical results are adjusted for changes in accounting policies and incorporate assumptions including the amount of future state, federal and foreign pretax operating income, the reversal of temporary differences, and the implementation of feasible and prudent tax‑planning strategies. These assumptions require significant judgment about the forecasts of future taxable income and are consistent with the plans and estimates the Company is using to manage the underlying businesses. In evaluating the objective evidence that historical results provide, three years of cumulative operating income (loss) are considered. Deferred income taxes have not been provided for U.S. tax liabilities or for additional foreign taxes on the unremitted earnings of foreign subsidiaries that have been indefinitely reinvested.
The calculation of the Company’s tax liabilities involves dealing with uncertainties in the application of complex tax laws and regulations in a multitude of jurisdictions across the Company’s global operations. Changes in tax laws and rates could also affect recorded deferred tax assets and liabilities in the future. The Company is not aware of any such changes that would have a material effect on the Company’s results of operations, cash flows, or financial position.
ASC Topic 740 provides that a tax benefit from an uncertain tax position may be recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, on the basis of the technical merits. ASC Topic 740 also provides guidance on measurement, derecognition, classification, interest and penalties, accounting in interim periods, disclosure, and transition.
The Company records tax liabilities in accordance with ASC Topic 740 and adjusts these liabilities when management’s judgment changes as a result of the evaluation of new information not previously available. Because of the complexity of some of these uncertainties, the ultimate resolution may result in payments that are different from the current estimates of these tax liabilities. These differences will be reflected as increases or decreases to income tax expense in the period in which new information becomes available.
Recently Issued Accounting Pronouncements
Subsequent to the adoption of the ASC, the FASB will issue Accounting Standards Updates (“ASUs”) as the means to add to or delete from, or otherwise amend the ASC. In 2014, prior to the issuance of the Company’s condensed consolidated financial statements, ASUs 2013-05 through 2014-15 have been issued. Following is a summary of recently issued ASUs that have affected or may affect the Company’s condensed consolidated financial statements:
		Affects	Status
ASU 2013-05		Foreign Currency Matters (Topic 830): Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity	Effective for fiscal periods beginning on or after December 15, 2013.
ASU 2014-06		Technical Corrections and Improvements Related to Glossary Terms	Effective on issuance in March 2014.
ASU 2014-09		Revenue from Contracts with Customers (Topic 606)	Effective for fiscal periods beginning on or after December 15, 2016
ASU 2014-11		Transfers and Servicing (Topic 860): Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures.	Effective for the first interim or annual period beginning after December 15, 2014
ASU 2014-12		Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period.	Effective for annual periods and interim periods within those annual periods beginning after December 15, 2015.
ASU 2014-15		Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern	Effective for the first interim or annual period ending after December 15, 2016
Adoption of those ASUs that became effective during 2014, prior to the issuance of the Company’s condensed consolidated financial statements, did not have a material effect on those financial statements.

Trading_Activities_And_Related

Trading Activities And Related Risks	9 Months Ended
	Sep. 30, 2014
Trading Activities And Related Risks [Abstract]	'
Trading Activities And Related Risks	'
	3. Trading Activities and Related Risks
	The Company’s trading activities include providing securities market making and brokerage services. Trading activities expose the Company to market and credit risks. These risks are managed in accordance with established risk management policies and procedures. To accomplish this, management has established a risk management process that includes:
	•a regular review of the risk management process by executive management as part of its oversight role;
	•defined risk management policies and procedures supported by a rigorous analytic framework; and
	•articulated risk tolerance levels as defined by executive management that are regularly reviewed to ensure that the Company’s risk‑taking is consistent with its business strategy, capital structure, and current and anticipated market conditions.
	Market Risk
	The Company is exposed to various market risks. Exposures to market risks arise from equity price risk, foreign currency exchange rate fluctuations and changes in interest rates. The Company seeks to mitigate market risk associated with trading inventories by employing hedging strategies that correlate rate, price and spread movements of trading inventories and related financing and hedging activities. The Company uses a combination of cash instruments and exchange traded derivatives to hedge its market exposures. The following discussion describes the types of market risk faced:
	Equity Price Risk
	Equity price risk arises from the possibility that equity security prices will fluctuate, affecting the value of equity securities and other instruments that derive their value from a particular stock, a defined basket of stocks, or a stock index. The Company is subject to equity price risk primarily in financial instruments held.  The Company attempts to limit such risks by continuously reevaluating prices and by diversifying its portfolio across many different options, futures and underlying securities and avoiding concentrations of positions based on the same underlying security.
	Currency Risk
	Currency risk arises from the possibility that fluctuations in foreign exchange rates will impact the value of financial instruments. The Company manages this risk using spot (i.e., cash) currency transactions, currency futures contracts and currency forward contracts.    As a global market maker trading on exchanges around the world in multiple currencies, we are exposed to foreign currency risk. We actively manage this exposure using hedging strategies that are based on a defined basket of 16 currencies we call the “GLOBAL”.  These strategies minimize the fluctuation of our net worth as expressed in GLOBALs, thereby diversifying our risk in alignment with these global currencies, weighted by our view of their importance. Because we report our financial results in U.S. dollars, the change in the value of the GLOBAL as expressed in U.S. dollars affects our earnings.
	Interest Rate Risk
	Interest rate risk arises from the possibility that changes in interest rates will affect the value of financial instruments. The Company is exposed to interest rate risk on cash and margin balances, positions carried in equity securities, options, and futures and on its debt obligations. These risks are managed through investment policies and by entering into interest rate futures contracts.
	Credit Risk
	The Company is exposed to risk of loss if an individual, counterparty or issuer fails to perform its obligations under contractual terms (“default risk”). Both cash instruments and derivatives expose the Company to default risk. The Company has established policies and procedures for mitigating credit risk on principal transactions, including reviewing and establishing limits for credit exposure, maintaining collateral, and continually assessing the creditworthiness of counterparties.
	The Company’s credit risk is limited in that substantially all of the contracts entered into are settled directly at securities and commodities clearing houses and a small portion is settled through member firms and banks with substantial financial and operational resources. The Company seeks to control the risks associated with its customer margin activities by requiring customers to maintain collateral in compliance with regulatory and internal guidelines.
	In the normal course of business, IBG, Inc. executes, settles, and finances various customer securities transactions. Execution of these transactions includes the purchase and sale of securities by the Company that exposes the Company to default risk arising from the potential that customers or counterparties may fail to satisfy their obligations. In these situations, the Company may be required to purchase or sell financial instruments at unfavorable market prices to satisfy obligations to customers or counterparties. Liabilities to other brokers and dealers related to unsettled transactions (i.e., securities fails to receive) are recorded at the amount for which the securities were purchased, and are paid upon receipt of the securities from other brokers or dealers. In the case of aged securities fails to receive, the Company may purchase the underlying security in the market and seek reimbursement for any losses from the counterparty.
	For cash management purposes, the Company enters into short‑term securities purchased under agreements to resell and securities sold under agreements to repurchase transactions (“repos”) in addition to securities borrowing and lending arrangements, all of which may result in credit exposure in the event the counterparty to a transaction is unable to fulfill its contractual obligations. Repos are collateralized by securities with a market value in excess of the obligation under the contract. Similarly, securities lending agreements are collateralized by deposits of cash or securities. The Company attempts to minimize credit risk associated with these activities by monitoring collateral values on a daily basis and requiring additional collateral to be deposited with or returned to the Company as permitted under contractual provisions.
	Concentrations of Credit Risk
	The Company’s exposure to credit risk associated with its trading and other activities is measured on an individual counterparty basis, as well as by groups of counterparties that share similar attributes. Concentrations of credit risk can be affected by changes in political, industry, or economic factors. To reduce the potential for risk concentration, credit limits are established and exposure is monitored in light of changing counterparty and market conditions. As of September 30, 2014, the Company did not have any material concentrations of credit risk.
	Off‑Balance Sheet Risks
	The Company may be exposed to a risk of loss not reflected in the condensed consolidated financial statements to settle futures and certain over‑the‑counter contracts at contracted prices, which may require repurchase or sale of the underlying products in the market at prevailing prices. Accordingly, these transactions result in off‑balance sheet risk as the Company’s cost to liquidate such contracts may exceed the amounts reported in the Company’s condensed consolidated statements of financial condition.

Equity_And_Earnings_Per_Share

Equity And Earnings Per Share	9 Months Ended
	Sep. 30, 2014
Equity And Earnings Per Share [Abstract]	'
Equity And Earnings Per Share	'
	4. Equity and Earnings Per Share
	In connection with IBG, Inc.’s initial public offering of Class A common stock (“IPO”) in May 2007, it purchased 10.0% of the membership interests in IBG LLC from IBG Holdings LLC (“Holdings”), became the sole managing member of IBG LLC and began to consolidate IBG LLC’s financial results into its financial statements. Holdings owns all of  IBG, Inc.’s Class B common stock, which has voting rights in proportion to its ownership interests in IBG LLC, approximately 85.9% as of September 30, 2014.  The condensed consolidated financial statements reflect the results of operations and financial position of IBG, Inc., including consolidation of its investment in IBG LLC and its subsidiaries. The noncontrolling interests in IBG LLC attributable to Holdings are reported as a component of total equity in the condensed consolidated statements of financial condition, as described below.
	Recapitalization and Post‑IPO Capital Structure
	Immediately prior to and immediately following the consummation of the IPO, IBG, Inc., Holdings, IBG LLC and the members of IBG LLC consummated a series of transactions collectively referred to herein as the “Recapitalization.” In connection with the Recapitalization, IBG, Inc., Holdings and the historical members of IBG LLC entered into an exchange agreement, dated as of May 3, 2007 (the “Exchange Agreement”), pursuant to which the historical members of IBG LLC received membership interests in Holdings in exchange for their membership interests in IBG LLC. Additionally, IBG, Inc. became the sole managing member of IBG LLC.
	In connection with the consummation of the IPO, Holdings used the net proceeds to redeem 10.0% of members’ interests in Holdings in proportion to their interests. Immediately following the Recapitalization and IPO, Holdings owned approximately 90% of IBG LLC and 100% of IBG, Inc.’s Class B common stock, which has voting power in IBG, Inc. in proportion to Holdings’ ownership of IBG LLC.
	Since consummation of the IPO and Recapitalization, IBG, Inc.’s equity capital structure has been comprised of Class A and Class B common stock. All shares of common stock have a par value of $0.01 per share and have identical rights to earnings and dividends and in liquidation. As described previously in this Note 4, Class B common stock has voting power in IBG, Inc. proportionate to the extent of Holdings’ and IBG, Inc.’s respective ownership of IBG LLC. At September 30, 2014 and December 31, 2013,  1,000,000,000 shares of Class A common stock were authorized, of which 57,247,149 and 54,788,049 shares have been issued; and 57,104,682 and 54,664,095 shares were outstanding, respectively. Class B common stock is comprised of 100 authorized shares, of which 100 shares were issued and outstanding as of September 30, 2014 and December 31, 2013, respectively. In addition, 10,000 shares of preferred stock have been authorized, of which no shares are issued or outstanding as of September 30, 2014 and December 31, 2013.
	As a result of a federal income tax election made by IBG LLC applicable to the acquisition of IBG LLC member interests by IBG, Inc., the income tax basis of the assets of IBG LLC acquired by IBG, Inc. have been adjusted based on the amount paid for such interests. Deferred tax assets were recorded as of the IPO date and in connection with the 2011 and 2013 redemptions of Holdings member interests in exchange for common stock, which deferred tax assets are included in other assets in the Company’s condensed consolidated statements of financial condition and are being amortized as additional deferred income tax expense over 15 years from the IPO date and from the 2011 and 2013 redemption dates, respectively, as allowable under current tax law. As of September 30, 2014 and December 31, 2013, the unamortized balance of these deferred tax assets was $277.9 million and $294.7 million, respectively.
	IBG, Inc. also entered into an agreement (the “Tax Receivable Agreement”) with Holdings to pay Holdings (for the benefit of the former members of IBG LLC) 85% of the tax savings that IBG, Inc. actually realizes as the result of tax basis increases. These payables, net of payments made to Holdings, are reported as payable to affiliate in the Company’s condensed consolidated statements of financial condition.    The remaining 15% is accounted for as a permanent increase to additional paid‑in capital in the Company’s condensed consolidated statements of financial condition.
	The cumulative amounts of deferred tax assets, payables to Holdings and credits to additional paid‑in capital arising from stock offerings from the date of the IPO through September 30, 2014 were $420.4 million, $357.4 million and $63.1 million, respectively. Amounts payable under the Tax Receivable Agreement are payable to Holdings annually following the filing of IBG, Inc.’s federal income tax return. The Company has paid Holdings a cumulative total of $86.2 million of which $15.7 million was paid in the nine months ended September 30, 2014, pursuant to the terms of the Tax Receivable Agreement.
	The Exchange Agreement, as amended June 6, 2012, provides for future redemptions of member interests and for the purchase of member interests in IBG LLC by IBG, Inc. from Holdings, which could result in IBG, Inc. acquiring the remaining member interests in IBG LLC that it does not own. On an annual basis, holders of Holdings member interests are able to request redemption of such member interests over a minimum eight (8) year period following the IPO; 12.5% annually for seven (7) years and 2.5% in the eighth year.
	At the time of the IBG, Inc.’s IPO in 2007, three hundred sixty (360) million shares of authorized Common Stock were reserved for future sales and redemptions. From 2008 through 2010, Holdings redeemed 5,013,259 IBG LLC shares with a total value of $114.0 million, which redemptions were funded using cash on hand at IBG LLC. Upon cash redemption these IBG LLC shares were retired. In 2011 and 2013, respectively, IBG, Inc. issued 1,983,624 shares and 4,683,415 shares of Common Stock directly to Holdings in exchange for an equivalent number of shares of member interests in IBG LLC.
	As a consequence of these redemption transactions, and distribution of shares to employees (see Note 9), IBG, Inc.’s interest in IBG LLC has increased to approximately 14.1%, with Holdings owning the remaining 85.9% as of September 30, 2014. The redemptions also resulted in an increase in the Holdings interest held by Thomas Peterffy and his affiliates from approximately 84.6% at the IPO to approximately 87.6% at September 30, 2014.
	On October 24, 2014, the Company issued 1,358,478 shares of Class A Common stock (with a fair value of $35.2 million) to Holdings in exchange for membership interests in IBG LLC equal in number to such number of shares of Common Stock issued by IBG, Inc. As a consequence of this transaction, IBG, Inc.’s interest in IBG LLC increased to approximately 14.5%, with Holdings owning the remaining 85.5%. The redemptions also resulted in an increase in the Holdings interest held by Thomas Peterffy and his affiliates from approximately 87.6% to approximately 88.0%.
	Earnings per Share
	Basic earnings per share are calculated utilizing net income available for common stockholders divided by the weighted average number of shares of Class A and Class B common stock outstanding for that period, presented in thousands, except shares and per share amounts:
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Basic earnings per share:
	Net income available for common stockholders	$	3,191	$	16,447	$	37,441	$	33,382
	Weighted average shares of common stock outstanding:
	Class A		57,098,952		49,965,950		55,956,515		48,807,221
	Class B		100		100		100		100
			57,099,052		49,966,050		55,956,615		48,807,321
	Basic earnings per share	$	0.06	$	0.33	$	0.67	$	0.68
	Diluted earnings per share are calculated utilizing the Company’s basic net income available for common stockholders divided by diluted weighted average shares outstanding with no adjustments to net income available to common stockholders for potentially dilutive common shares, presented in thousands, except shares and per share amounts:
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Diluted earnings per share:
	Net income available for common stockholders	$	3,191	$	16,447	$	37,441	$	33,382
	Weighted average shares of common stock outstanding:
	Class A:
	Issued and outstanding		57,098,952		49,965,950		55,956,515		48,807,221
	Potentially dilutive common shares issuable pursuant to employee incentive plans		1,121,018		1,022,164		1,239,498		1,174,343
	Class B		100		100		100		100
			58,220,070		50,988,214		57,196,113		49,981,664
	Diluted earnings per share	$	0.05	$	0.32	$	0.65	$	0.67
	Member Distributions and Stockholder Dividends
	For the nine months ended September 30, 2014, IBG LLC made distributions totaling $283.1 million to its members, of which IBG, Inc.’s proportionate share was $39.0 million.  In March, June and September 2014, the Company paid cash dividends of $0.10 per share of Common Stock, totaling $5.5 million, $5.7 million and $5.7 million, respectively.
	On October 21, 2014, the Company declared a cash dividend of $0.10 per common share, payable on December 12, 2014 to shareholders of record as of December 1, 2014.

Comprehensive_Income

Comprehensive Income	9 Months Ended
	Sep. 30, 2014
Comprehensive Income Detail [Abstract]	'
Comprehensive Income	'
	5. Comprehensive Income
	The following table presents comprehensive income and earnings per share on comprehensive income, presented in thousands, except shares and per share amounts:
		Three months ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Comprehensive income (loss) available for common stockholders, net of tax	$	-7,594	$	20,077	$	28,502	$	29,666
	Earnings per share on comprehensive income:
	Basic	$	-0.13	$	0.40	$	0.51	$	0.61
	Diluted	$	-0.13	$	0.39	$	0.50	$	0.59
	Weighted average common shares outstanding:
	Basic		57,099,052		49,966,050		55,956,615		48,807,321
	Diluted		58,220,070		50,988,214		57,196,113		49,981,664

Financial_Assets_And_Financial

Financial Assets And Financial Liabilities	9 Months Ended
	Sep. 30, 2014
Financial Assets And Financial Liabilities [Abstract]	'
Financial Assets And Financial Liabilities	'
	6. Financial Assets and Financial Liabilities
	Fair Value
	The following tables set forth, by level within the fair value hierarchy (see Note 2), financial assets and liabilities, primarily financial instruments owned, at fair value, financial instruments sold, but not yet purchased, at fair value, and other assets and liabilities measured at fair value on a recurring basis as of September 30, 2014 and December 31, 2013, presented in thousands. As required by ASC Topic 820, financial assets and financial liabilities are classified in their entirety based on the lowest level of input that is significant to the respective fair value measurement.
			Financial Assets At Fair Value as of September 30, 2014
			Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes		$	4,577,342		$	-		$	-		$	4,577,342
	Financial instruments owned:
	Stocks			836,551			-			106			836,657
	Options			1,255,124			-			-			1,255,124
	Warrants and discount certificates			44,099			-			-			44,099
	U.S. and foreign government securities			14,686			1,386			-			16,072
	Corporate and municipal bonds			68,735			11,565			-			80,300
	Currency forward contracts			-			4,601			-			4,601
	Total financial instruments owned			2,219,195			17,552			106			2,236,853
	Financial instruments owned and pledged as collateral:
	Stocks			1,070,314			-			-			1,070,314
	Warrants			307			-			-			307
	U.S. and foreign government securities			87,727			-			-			87,727
	Corporate and municipal bonds			975			-			-			975
	Total financial instruments owned and pledged as collateral			1,159,323			-			-			1,159,323
	Total financial instruments owned, at fair value			3,378,518			17,552			106			3,396,176
	Other fair value investments, included in other assets:
	Stocks and options			34,441			-			162			34,603
	Corporate and municipal bonds			-			1,567			-			1,567
	Total other fair value investments, included in other assets			34,441			1,567			162			36,170
	Total Financial Assets at Fair Value		$	7,990,301		$	19,119		$	268		$	8,009,688
			Financial Liabilities At Fair Value as of September 30, 2014
			Level 1			Level 2			Level 3			Total
	Financial instruments sold,  but not yet purchased, at fair value:
	Stocks		$	1,242,103		$	-		$	76		$	1,242,179
	Options			1,317,944			-			-			1,317,944
	Warrants and discount certificates			760			-			-			760
	U.S. and foreign government securities			-			1,648			-			1,648
	Corporate bonds			78,206			8,452			-			86,658
	Currency forward contracts			-			475			-			475
	Total financial instruments sold, but not yet purchased, at fair value			2,639,013			10,575			76			2,649,664
	Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities
	Stocks and options			64			-			-			64
	Total other fair value liabilities, included in accounts payable, accrued expenses and other liabilities			64			-			-			64
	Total Financial Liabilities at Fair Value		$	2,639,077		$	10,575		$	76		$	2,649,728
				Financial Assets At Fair Value as of December 31, 2013
				Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes			$	1,300,016		$	-		$	-		$	1,300,016
	Financial instruments owned:
	Stocks				1,243,914			-			57			1,243,971
	Options				1,880,481			-			-			1,880,481
	Warrants and discount certificates				57,144			-			-			57,144
	U.S. and foreign government securities				4,641			2,102			-			6,743
	Corporate and municipal bonds				72,750			18,476			-			91,226
	Currency forward contracts				-			5,748			-			5,748
	Total financial instruments owned				3,258,930			26,326			57			3,285,313
	Financial instruments owned and pledged as collateral:
	Stocks				1,097,734			-			-			1,097,734
	Warrants				233			-			-			233
	U.S. and foreign government securities				64,439			-			-			64,439
	Corporate and municipal bonds				1,125			-			-			1,125
	Total financial instruments owned and pledged as collateral				1,163,531			-			-			1,163,531
	Total financial instruments owned, at fair value				4,422,461			26,326			57			4,448,844
	Other fair value investments, included in other assets:
	Stocks				25,604			419			101			26,124
	Corporate and municipal bonds				1,776			47,896			-			49,672
	Mortgage backed securities				-			26,892			-			26,892
	Other asset backed securities				-			22,734			-			22,734
Other				-			5,328			-			5,328
Total other fair value investments, included in other assets				27,380			103,269			101			130,750
Total Financial Assets at Fair Value			$	5,749,857		$	129,595		$	158		$	5,879,610
		Financial Liabilities At Fair Value as of December 31, 2013
		Level 1			Level 2			Level 3			Total
Financial instruments sold, but not yet purchased, at fair value:
Stocks		$	1,266,429		$	-		$	3		$	1,266,432
Options			1,793,248			-			-			1,793,248
Warrants and discount certificates			1,215			-			-			1,215
U.S. and foreign government securities			-			4,412			-			4,412
Corporate bonds			77,936			9,628			-			87,564
Currency forward contracts			-			802			-			802
Total financial instruments sold, but not yet purchased, at fair value		$	3,138,828		$	14,842		$	3		$	3,153,673
Transfers between Level 1 and Level 2
Transfers of financial instruments owned and sold, but not yet purchased, at fair value to or from Levels 1 and 2 arise where the market for a specific security has become active or inactive during the period. The fair values transferred are ascribed as if the financial assets or financial liabilities had been transferred as of the end of the period.
During the nine months ended September 30, 2014, the Company reclassified approximately $1.7 million of financial instruments owned, at fair value from Level 1 to Level 2 and reclassified approximately $4.7 million from Level 2 to Level 1. Financial instruments sold, but not yet purchased, at fair value of approximately $1.1 million were reclassified from Level 1 to Level 2 and approximately $1.3 million were reclassified from Level 2 to Level 1. The Company reclassified approximately $1.5 million of other fair value investments, included in other assets, from Level 1 to Level 2.
During the nine months ended September 30, 2013, the Company reclassified approximately $1.7 million of financial instruments owned, at fair value from Level 1 to Level 2 and reclassified approximately $1.4 million from Level 2 to Level 1.  Financial instruments sold, but not yet purchased, at fair value of approximately $1.3 million were reclassified from Level 1 to Level 2 and approximately $1.5 million were reclassified from Level 2 to Level 1.
Level 3 Financial Assets and Financial Liabilities
The Company’s Level 3 financial assets and financial liabilities are comprised of delisted securities reported within financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value in the condensed consolidated statements of financial condition. The following tables report Level 3 activities for the nine months ended September 30, 2014 and September 30, 2013, presented in thousands:
Financial assets and liabilities—Level 3 activities:
		Financial Assets			Financial Liabilities
Balance, January 1, 2014		$	158		$	3
Total gains or losses (realized/unrealized)  - Included in earnings			99			-
Purchases, issuances and settlements			-44			-
Transfers in and/or out of Level 3			55			73
Balance, September 30, 2014		$	268		$	76
		Financial Assets			Financial Liabilities
Balance, January 1, 2013		$	-		$	-
Total gains or losses (realized/unrealized) - Included in earnings			-184			77
Purchases, issuances and settlements			-			-
Transfers in and/or out of Level 3			365			-13
Balance, September 30, 2013		$	181		$	64
Trading Gains (Losses) from Market Making Transactions
Trading gains and losses from market making transactions reported in the statements of comprehensive income, by major product type, are presented in thousands and comprised of:
		Three Months Ended						Nine months Ended
		September 30,						September 30,
		2014			2013			2014			2013
Equities		$	44,731		$	65,562		$	196,440		$	227,078
Fixed Income			5,706			4,449			17,797			18,920
Foreign Exchange			-126,130			53,275			-78,398			-44,727
Commodities			-			-			-			115
Total Trading gains (losses)		$	-75,693		$	123,286		$	135,839		$	201,386
These transactions are related to the Company’s financial instruments owned and financial instruments sold, but not yet purchased,  at fair value and include both derivative and non‑derivative financial instruments, including exchange traded options and futures. These gains and losses also include market making related dividend and fixed income trading related interest income and expense.
The gains (losses) in the above table are not representative of the integrated trading strategies applied by the Company, which utilizes financial instruments across various product types. Gains and losses in one product type frequently offset gains and losses in other product types.
Netting of Financial Assets and Financial Liabilities
The Company adopted the guidance in ASU 2011‑11, Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities (“ASU 2011-11”) and ASU 2013‑ 01, Balance Sheet (Topic 210): Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities (“ASU 2013-01”) for periods beginning after January 1, 2013. This authoritative guidance requires companies to report disclosures of offsetting assets and liabilities.
The Company does not net securities segregated for regulatory purposes, In addition, securities borrowed and securities loaned, and securities purchased under agreements to resell and securities sold under agreements to repurchase, are presented on a gross basis in the condensed consolidated statements of financial condition. In the tables below, the amounts of derivative financial instruments owned that are not offset in the condensed consolidated statements of financial condition, but could be netted against financial liabilities with specific counterparties under master netting agreements, including clearing houses (exchange traded options, warrants and discount certificates) or over the counter currency forward contract counterparties, are presented to provide financial statement readers with the Company’s estimate of its net exposure to counterparties for these derivative financial instruments.
The following tables, presented in millions, sets forth the netting of financial assets and of financial liabilities as of September 30, 2014 and December 31, 2013, pursuant to the requirements of ASU 2011‑11 and ASU 2013‑01.
		30-Sep-14
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
Offsetting of Financial Assets:
Securities segregated for regulatory purposes -purchased under agreements to resell		$	5,253.2	1		$	-		$	5,253.2		$	-5,253.20	$	-	$	-
Securities borrowed			2,955.1				-			2,955.1			-2,868.10		-		87.0
Securities purchased under agreements to resell			273.5				-			273.5			-273.5		-		-
Financial Instruments owned, at fair value:			-										-
Options			1,255.1				-			1,255.1			-1,206.30		-		48.8
Warrants and discount certificates			44.4				-			44.4			-0.8		-		43.6
Currency forward contracts			4.6				-			4.6			-		-		4.6
Total		$	9,785.9			$	-		$	9,785.9		$	-9,601.90	$	-	$	184.0
									Net Amounts of			Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
Offsetting of Financial Liabilities:
Securities loaned		$	3,116.4			$	-		$	3,116.4		$	-3,114.50	$	-	$	1.9
Financial instruments sold, but not yet purchased, at fair value:
Options			1,318.0				-			1,318.0			-1,206.30		-		111.7
Warrants and discount certificates			0.8				-			0.8			-0.8		-		-
Currency forward contracts			0.5				-			0.5			-		-		0.5
Total		$	4,435.7			$	-		$	4,435.7		$	-4,321.60	$	-	$	114.1
		31-Dec-13
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
Offsetting of Financial Assets:
Securities segregated for regulatory purposes - purchased under agreements to resell		$	6,734.2	1		$	-		$	6,734.2		$	-6,734.20	$	-	$	-
Securities borrowed			2,751.5				-			2,751.5			-2,694.60		-		56.9
Securities purchased under agreements to resell			386.3				-			386.3			-386.3		-		-
Financial Instruments owned, at fair value:
Options			1,880.5				-			1,880.5			-1,652.80		-		227.7
Warrants and discount certificates			57.4				-			57.4			-1.2		-		56.2
Currency forward contracts			5.7				-			5.7			-		-		5.7
Total		$	11,815.6			$	-		$	11,815.6		$	-11,469.10	$	-	$	346.5
									Net Amounts of				Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
Offsetting of Financial Liabilities:
Securities loaned		$	2,563.7			$	-		$	2,563.7		$	-2,544.60	$	-	$	19.1
Financial instruments sold, but not yet purchased, at fair value:
Options			1,793.2				-			1,793.2			-1,652.80		-		140.4
Warrants and discount certificates			1.2				-			1.2			-1.2		-		-
Currency forward contracts			0.8				-			0.8			-		-		0.8
Total		$	4,358.9			$	-		$	4,358.9		$	-4,198.60	$	-	$	160.3
	-1		As of September 30, 2014 and December 31, 2013, the Company had $5.25 billion and $6.73 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in “Cash and securities—segregated for regulatory purposes” in the condensed consolidated statements of financial condition.

Collateralized_Transactions

Collateralized Transactions	9 Months Ended
	Sep. 30, 2014
Disclosure Collateralized Transactions [Abstract]	'
Collateralized Transactions	'
	7. Collateralized Transactions
	The Company enters into securities borrowing and lending transactions and agreements to repurchase and resell securities to finance trading inventory, to obtain securities for settlement and to earn residual interest rate spreads. In addition, the Company’s customers pledge their securities owned to collateralize margin loans. Under these transactions, the Company either receives or provides collateral, including equity, corporate debt and U.S. government securities. Under many agreements, the Company is permitted to sell or repledge securities received as collateral and use these securities to secure securities purchased under agreements to resell, enter into securities lending transactions or deliver these securities to counterparties to cover short positions.
	The Company also engages in securities financing transactions with and for customers through margin lending. Customer receivables generated from margin lending activity are collateralized by customer‑owned securities held by the Company. Customers’ required margin levels and established credit limits are monitored continuously by risk management staff using automated systems. Pursuant to the Company’s policy and as enforced by such systems, customers are required to deposit additional collateral or reduce positions, when necessary to avoid automatic liquidation of their positions.
	Margin loans are extended to customers on a demand basis and are not committed facilities. Factors considered in the acceptance or rejection of margin loans are the amount of the loan, the degree of leverage being employed in the customer account and an overall evaluation of the customer’s portfolio to ensure proper diversification or, in the case of concentrated positions, appropriate liquidity of the underlying collateral. Additionally, transactions relating to concentrated or restricted positions are limited or prohibited by raising the level of required margin collateral (to 100% in the extreme case). Underlying collateral for margin loans is evaluated with respect to the liquidity of the collateral positions, valuation of securities, volatility analysis and an evaluation of industry concentrations. Adherence to the Company’s collateral policies significantly limits the Company’s credit exposure to margin loans in the event of a customer’s default. Under margin lending agreements, the Company may request additional margin collateral from customers and may sell securities that have not been paid for or purchase securities sold but not delivered from customers, if necessary. At September 30, 2014 and December 31, 2013, approximately $17.26 billion and $13.60 billion, respectively, of customer margin loans were outstanding.
	The following table, presented in millions, summarizes the amounts related to collateralized transactions at September 30, 2014 and December 31, 2013:
			30-Sep-14				31-Dec-13
			Permitted		Sold or		Permitted		Sold or
			to Repledge		Repledged		to Repledge		Repledged
	Securities lending transactions		$	9,593.3	$	1,408.9	$	9,331.9	$	2,504.3
	Agreements to resell 1			5,527.5		5,524.2		7,116.1		7,099.6
	Customer margin assets			15,365.2		3,797.3		11,753.3		4,602.9
			$	30,486.0	$	10,730.4	$	28,201.3	$	14,206.8
		-1		At September 30, 2014, $5.25 billion or 95% (at December 31, 2013, $6.73 billion, or 95%) of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.
	In the normal course of business, the Company pledges qualified securities with clearing organizations to satisfy daily margin and clearing fund requirements. At September 30, 2014 and December 31, 2013, the majority of the Company’s U.S. and foreign government securities owned were pledged to clearing organizations.
	Financial instruments owned and pledged as collateral, including amounts pledged to affiliates, where the counterparty has the right to repledge, at September 30, 2014 and December 31, 2013 are presented in the following table in millions:
			September 30,		December 31,
			2014		2013
	Stocks		$	1,070.3	$	1,097.8
	Warrants			0.3		0.2
	U.S. and foreign government securities			87.7		64.4
	Corporate and municipal bonds			1.0		1.1
			$	1,159.3	$	1,163.5

Senior_Secured_Revolving_Credi

Senior Secured Revolving Credit Facility	9 Months Ended
	Sep. 30, 2014
Senior Secured Revolving Credit Facility [Abstract]	'
Senior Secured Revolving Credit Facility	'
	8. Senior Secured Revolving Credit Facility
	On May 17, 2012, IBG LLC entered into a $100 million three‑year senior secured revolving credit facility with Bank of America, N.A. as administrative agent and Citibank, N.A., as syndication agent. This credit facility replaced a similar two‑year facility that expired on May 18, 2012.  On August 8, 2014 IBG LLC elected to terminate this credit facility.

Employee_Incentive_Plans

Employee Incentive Plans	9 Months Ended
	Sep. 30, 2014
Employee Incentive Plans [Abstract]	'
Employee Incentive Plans	'
	9. Employee Incentive Plans
	Return on Investment Dollar Units (“ROI Dollar Units”)
	From 1998 through January 1, 2006, IBG LLC granted all non‑member employees ROI Dollar Units, which are redeemable under the amended provisions of the plan, and in accordance with regulations issued by the Internal Revenue Service (Section 409A of the Internal Revenue Code). Upon redemption, the grantee is entitled to accumulated earnings on the face value of the certificate, but not the actual face value. For grants made in 1998 and 1999, grantees may redeem the ROI Dollar Units after vesting on the fifth anniversary of the date of their grant and prior to the tenth anniversary of the date of their grant. For grants made between January 1, 2000 and January 1, 2005, grantees must elect to redeem the ROI Dollar Units upon the fifth, seventh or tenth anniversary date. These ROI Dollar Units have vested at the fifth anniversary of the date of their grant and will continue to accumulate earnings until the elected redemption date. For grants made on or after January 1, 2006, all ROI Dollar Units vested on the fifth anniversary date of their grant and were or will be automatically redeemed. Subsequent to the IPO, no additional ROI Dollar Units have been or will be granted, and non‑cash compensation to employees will consist primarily of grants of shares of common stock as described below under “2007 Stock Incentive Plan.”
	As of September 30, 2014 and December 31, 2013, payables to employees for ROI Dollar Units were $3.1 million and $5.6 million, respectively, all of which were vested. These amounts are included in accounts payable, accrued expenses and other liabilities in the condensed consolidated statements of financial condition. Compensation expense for the ROI Dollar Unit plan, included in the condensed consolidated statements of comprehensive income was $0.2 million and $0.5 million for the nine months ended September 30, 2014 and 2013, respectively.
	2007 ROI Unit Stock Plan
	In connection with the IPO, the Company adopted the Interactive Brokers Group, Inc. 2007 ROI Unit Stock Plan (the “ROI Unit Stock Plan”). Under this plan, certain employees of IBG LLC who held ROI Dollar Units, at the employee’s option, elected to invest their ROI Dollar Unit accumulated earnings as of December 31, 2006 in shares of common stock. An aggregate of 1,271,009 shares of common stock (consisting of 1,250,000 shares issued under the ROI Unit Stock Plan and 21,009 shares under the 2007 Stock Incentive Plan, as described below), with a fair value at the date of grant of $38.1 million were issued to IBG LLC and held as treasury stock, to be distributed to employees in accordance with the following schedule and subject to the conditions below:
	•10% on the date of the IPO (or on the first anniversary of the IPO, in the case of U.S. ROI Unit holders who made the above-referenced elections after December 31, 2006); and
	•an additional 15% on each of the first six anniversaries of the date of the IPO, assuming continued employment with the Company and compliance with other applicable covenants.
	Of the fair value at the date of grant, $17.8 million represented the accumulated ROI Dollar Unit value elected to be invested by employees in common stock and such amount was accrued for as of December 31, 2006. The remainder is being ratably accrued as compensation expense by the Company from the date of the IPO over the requisite service period represented by the aforementioned distribution schedule
	As of December 31, 2012, compensation costs for the ROI Unit Stock Plan had been fully accrued.  As of September 30, 2014, the Company still has 13,022 shares of common stock to be distributed to former employees under the ROI Unit Stock Plan.
	2007 Stock Incentive Plan
	Under the Company’s 2007 Stock Incentive Plan (the “Stock Incentive Plan”), up to 30 million shares (20 million shares at December 31, 2013) of the Company’s common stock may be granted and issued to directors, officers, employees, contractors and consultants of the Company.  The 10 million increase in shares allocated to the Stock Incentive Plan was approved by the Company’s Compensation Committee and Board of Directors in February 2014.  The Board of Directors’ approval was ratified by a vote of the stockholders at the Company’s 2014 Annual Meeting held on April 24, 2014.  The purpose of the Stock Incentive Plan is to promote the Company’s long‑term financial success by attracting, retaining and rewarding eligible participants.
	As a result of the Company’s organizational structure, a description of which can be found on page 4 of the Company’s 2013 Annual Report on Form 10-K, filed with the SEC, there is no dilutive effect upon ownership of minority stockholders of issuing shares under the Stock Incentive Plan.  The issuances do not dilute the book value of the ownership of minority stockholders because a) the restricted stock units are granted at market value and b) upon their vesting and the related issuance of shares of Common stock, the ownership of the Company in its operating subsidiary, IBG LLC, increases proportionately to the shares issued. As a result of such proportionate increase in share ownership, the dilution upon issuance of common stock is borne by IBG LLC’s majority member (i.e., noncontrolling interest), Holdings, and not by the Company or its minority shareholders. Additionally, dilution of earnings that may take place after issuance of common stock is reflected in EPS reported in the Company’s financial statements. The EPS dilution can be neither estimated nor projected, but historically it has not been material.
	The Stock Incentive Plan is administered by the Compensation Committee of the Company’s Board of Directors. The Compensation Committee has discretionary authority to determine which employees are eligible to participate in the Stock Incentive Plan and establishes the terms and conditions of the stock awards, including the number of awards granted to each employee and all other terms and conditions applicable to such awards in individual grant agreements. Awards are expected to be made primarily through grants of restricted common stock. Stock Incentive Plan awards are subject to issuance over time and may be forfeited upon an employee’s termination of employment or violation of certain applicable covenants prior to issuance, unless determined otherwise by the Compensation Committee.
	The Stock Incentive Plan provides that, upon a change in control, the Compensation Committee may, at its discretion, fully vest any granted but not yet earned awards under the Stock Incentive Plan, or provide that any such granted but not yet earned awards will be honored or assumed, or new rights substituted therefore by the new employer on a substantially similar basis and on terms and conditions substantially comparable to those of the Stock Incentive Plan.
	The Company granted awards under the Stock Incentive Plan in connection with the IPO and is expected to continue to grant awards on or about December 31 of each year following the IPO, to eligible employees as part of an overall plan of equity compensation. Shares of common stock vest, and become distributable to employees in accordance with the following schedule:
	•10% on the first vesting date, which approximates the anniversary of the IPO; and
	•an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with the Company and compliance with non-competition and other applicable covenants.
	Awards granted to external directors vest, and are distributed, over a five‑year period (20% per year) commencing one year after the date of grant. A total of 20,423 shares have been granted to the external directors cumulatively since the IPO.
	Stock Incentive Plan share grants (excluding 21,009 shares issued pursuant to the ROI Unit Stock Plan described above) and the related fair values at the date each of grant are presented in the table below:
					Fair Value at
					Date of Grant
			Shares		($ millions)
	In connection with IPO		927,943		$	27.8
	31-Jul-07		16,665			0.4
	31-Dec-07		1,055,206			32.9
	31-Dec-08		2,065,432			35.6
	31-Dec-09		2,448,031			42.8
	31-Dec-10		2,513,738			43.2
	31-Dec-11		3,411,613			50.8
	6-Jan-12		1,215,866			18.4
	31-Dec-12		3,629,960			50.5
	31-Dec-13		1,894,046			46.2
			19,178,500		$	348.6
	Estimated future grants under the Stock Incentive Plan are accrued for ratably during each year (Note 2).  In accordance with the vesting schedule, outstanding awards vest and are distributed to participants once each year on or about the Company’s IPO anniversary. At the end of each year, there are no vested awards that remain undistributed.
	Compensation expense related to the Stock Incentive Plan recognized in the condensed consolidated statements of comprehensive income was $31.5 million and $28.1 million for the nine months ended September 30, 2014 and 2013, respectively. Estimated future compensation costs for unvested awards, net of forfeiture credits, at September 30, 2014 are $26.4 million.
	The following summarizes the Stock Incentive Plan and ROI Unit Stock Plan activities for the nine months ended September 30, 2014.
			Shares		Shares
			Stock		ROI Unit
			Incentive Plan		Stock Plan
	Balance, December 31, 2013		11,647,117		-
	Granted		-		-
	Forfeited 1		-507,858		15,518
	Distributed		-2,438,091		-2,496
	Balance, September 30, 2014		8,701,168		13,022
		-1		ROI Unit Stock Plan number of forfeited shares related to prior years was adjusted by 15,518 shares during the period.
	Awards granted under the stock plans are subject to forfeiture in the event an employee ceases employment with the Company. The stock plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted. Distributions of remaining awards granted on or before January 1, 2009 to former employees will occur within 90 days of the anniversary of the termination of employment date over a five (5) year vesting schedule, 12.5% in each of the first four years and 50% in the fifth year. Distributions of remaining awards granted on or after January 1, 2010 to former employees will occur over the remaining vesting schedule applicable to each grant. Through September 30, 2014, a total of 179,246 shares have been distributed under these post‑employment provisions. These distributions are included in the table above.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Taxes [Abstract]	'
Income Taxes	'
	10. Income Taxes
	Income tax expense for the nine months ended September 30, 2014 and 2013 differs from the U.S. federal statutory rate primarily due to the taxation treatment of income attributable to noncontrolling interests in IBG LLC.  These noncontrolling interests are subject to U.S. taxation as partnerships.  Accordingly, the income attributable to these noncontrolling interests is reported in the condensed consolidated statements of comprehensive income, but the related U.S. income tax expense attributable to these noncontrolling interests is not reported by the Company as it is the obligation of the individual partners.  Income tax expense is also affected by the differing effective tax rates in foreign, state and local jurisdictions where certain of the Company’s subsidiaries are subject to corporate taxation.
	Deferred income taxes arise primarily due to the amortization of the deferred tax assets recognized in connection with the common stock offerings (see Note 4), differences in the valuation of financial assets and liabilities, and for other temporary differences arising from the deductibility of compensation and depreciation expenses in different time periods for book and income tax return purposes.
	As of and for the nine months ended September 30, 2014 and 2013, the Company had no unrecognized tax liabilities as defined under ASC Topic 740 and no valuation allowances on deferred tax assets were required. The Company is subject to taxation in the U.S. and various states and foreign jurisdictions. As of September 30, 2014, the Company is open to U.S. Federal and State income tax examinations for the tax years 2010 through 2012, and to non U.S. income tax examinations for the tax years 2006 through 2013.
	At September 30, 2014, accumulated earnings held by non‑U.S. subsidiaries totaled $1,091.1 million (at December 31, 2013 $1,072.9 million). Of this amount, approximately $414.0 million (at December 31, 2013 $422.3 million) is attributable to earnings of the Company’s foreign subsidiaries that are considered “pass‑through” entities for U.S. income tax purposes. Since the Company accounts for U.S. income taxes on these earnings on a current basis, no additional U.S. tax consequences would result from the repatriation of these earnings other than that which would be due arising from currency fluctuations between the time the earnings are reported for U.S. tax purposes and when they are remitted. With respect to certain of these subsidiaries’ accumulated earnings (approximately $309.0 million and $318.7 million as of September 30, 2014 and December 31, 2013, respectively), repatriation would result in additional foreign taxes in the form of dividend withholding tax imposed on the recipient of the distribution or dividend distribution tax imposed on the payor of the distribution. The Company has not provided for its proportionate share of these additional foreign taxes as it does not intend to repatriate these earnings in the foreseeable future. For the same reason, the Company has not provided deferred U.S. tax on cumulative translation adjustments associated with these earnings.
	The remainder of the accumulated earnings are attributable to non‑U.S. subsidiaries that are not considered “pass‑through” entities for U.S. tax purposes.  The Company’s U.S. tax basis in the stock of most of these entities exceeds its book basis. Establishing a deferred tax asset pursuant to ASC Topic 740 is not permitted as this difference will not reverse in the foreseeable future. In the instances in which the Company’s book basis exceeds its U.S. tax basis, no deferred tax liability has been established as the Company considers the earnings of those entities to be indefinitely reinvested.

Commitments_Contingencies_And_

Commitments, Contingencies And Guarantees	9 Months Ended
	Sep. 30, 2014
Commitments, Contingencies And Guarantees [Abstract]	'
Commitments, Contingencies And Guarantees	'
	11. Commitments, Contingencies and Guarantees
	In October 2013, a small number of the Company’s brokerage customers had taken relatively large positions in four stocks listed on the Singapore Exchange. In early October, within a very short timeframe, these securities lost over 90% of their value. The customer accounts were margined and fell into deficits totaling $64 million prior to the time the Company took possession of their securities positions. The Company has recognized a cumulative loss of approximately $82.0 million from October 2013 through September 30, 2014. The maximum aggregate loss, which would occur if the securities’ prices all fell to zero and none of the debts were collected, would be approximately $84 million. The Company is currently pursuing the collection of the debts. The ultimate effect of this incident on the Company’s results will depend upon market conditions and the outcome of the Company’s debt collection efforts.
	Litigation
	The Company is subject to certain pending and threatened legal actions which arise out of the normal course of business. Litigation is inherently unpredictable, particularly in proceedings where claimants seek substantial or indeterminate damages, or which are in their early stages. The Company has not been able to quantify the actual loss or range of loss related to such legal proceedings, the manner in which they will be resolved, the timing of final resolution or the ultimate settlement. Management believes that the resolution of these actions will not have a material effect, if any, on the Company’s business or financial condition, but may have a material impact on the results of operations for a given period.
	The Company accounts for potential losses related to litigation in accordance with FASB ASC Topic 450, “Contingencies.” As of September 30, 2014 and December 31, 2013, reserves provided for potential losses related to litigation matters were not material.
	Guarantees
	Certain of the Operating Companies provide guarantees to securities clearing houses and exchanges which meet the accounting definition of a guarantee under FASB ASC Topic 460, “Guarantees.” Under standard membership agreements, clearing house and exchange members are required to guarantee collectively the performance of other members. Under the agreements, if a member becomes unable to satisfy its obligations, other members would be required to meet shortfalls. In the opinion of management, the Operating Companies’ liability under these arrangements is not quantifiable and could exceed the cash and securities they have posted as collateral. However, the potential for these Operating Companies to be required to make payments under these arrangements is remote. Accordingly, no contingent liability is carried in the condensed consolidated statements of financial condition for these arrangements.
	In connection with its retail brokerage business, IB LLC or other electronic brokerage Operating Companies perform securities and commodities execution, clearance and settlement on behalf of their customers for whom they commit to settle trades submitted by such customers with the respective clearing houses. If a customer fails to fulfill its settlement obligations, the respective Operating Company must fulfill those settlement obligations. No contingent liability is carried on the condensed consolidated statements of financial condition for such customer obligations.
	Other Commitments
	Certain clearing houses and clearing banks and firms used by certain Operating Companies are given a security interest in certain assets of those Operating Companies held by those clearing organizations. These assets may be applied to satisfy the obligations of those Operating Companies to the respective clearing organizations.

Segment_And_Geographic_Informa

Segment And Geographic Information	9 Months Ended
	Sep. 30, 2014
Segment And Geographic Information [Abstract]	'
Segment And Geographic Information	'
	12. Segment and Geographic Information
	The Company operates in two business segments: electronic brokerage and market making. The Company conducts its electronic brokerage business through its Interactive Brokers subsidiaries, which provide electronic execution and clearing services to customers worldwide. The Company conducts its market making business principally through its Timber Hill subsidiaries on the world’s leading exchanges and market centers, primarily in exchange‑traded equities, equity options and equity‑index options and futures.
	Significant transactions and balances between the Operating Companies occur, primarily as a result of certain Operating Companies holding exchange or clearing organization memberships, which are utilized to provide execution and clearing services to affiliates. Charges for transactions between segments are designed to approximate full costs.  Intra‑segment and intra‑region income and expenses and related balances have been eliminated in this segment and geographic information to reflect the external business conducted in each segment or geographical region. Corporate items include non‑allocated corporate income and expenses that are not attributed to segments for performance measurement, corporate assets and eliminations.
	Management believes that the following information by business segment provides a reasonable representation of each segment’s contribution to total net revenues and income before income taxes for the three and nine months ended September 30, 2014 and 2013, and total assets as of September 30, 2014 and December 31, 2013, presented in millions.
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Net revenues:
	Electronic brokerage	$	243.0	$	194.7	$	687.3	$	602.5
	Market making		-70.4		130.9		154.6		221.9
	Corporate and eliminations		-1.6		0.7		-6.7		1.9
	Total net revenues	$	171.0	$	326.3	$	835.2	$	826.3
	Income before income taxes:
	Electronic brokerage	$	152.4	$	108.4	$	418.1	$	342.7
	Market making		-111.8		87.5		22.8		66.1
	Corporate and eliminations		-1.1		0.5		-9.1		3.7
	Total income before income taxes	$	39.5	$	196.4	$	431.8	$	412.5
		September 30,		December 31,
		2014		2013
	Assets:
	Electronic brokerage	$	36,125.0	$	31,333.5
	Market making		11,910.7		12,139.5
	Corporate and eliminations		-6,427.50		-5,602.30
	Total assets	$	41,608.2	$	37,870.7
	The Company operates its automated global business in U.S. and international markets on more than 100 exchanges and market centers. A significant portion of the Company’s net revenues are generated by subsidiaries operating outside the U.S. International operations are comprised of electronic brokerage and market making activities in 24 countries in Europe, Asia and the Americas (outside the U.S.). The following table presents total net revenues and income before income taxes by geographic area for the three and nine months ended September 30, 2014 and 2013, presented in millions.
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Net revenues:
	United States	$	123.2	$	265.4	$	658.5	$	597.3
	International		66.3		59.5		201.1		227.2
	Corporate and eliminations		-18.4		1.4		-24.3		1.8
	Total net revenues	$	171.1	$	326.3	$	835.3	$	826.3
	Income before income taxes:
	United States	$	29.9	$	180.9	$	392.0	$	331.9
	International		12.6		14.3		51.4		76.9
	Corporate and eliminations		-3		1.2		-11.6		3.7
	Total income before income taxes	$	39.5	$	196.4	$	431.8	$	412.5

Regulatory_Requirements

Regulatory Requirements	9 Months Ended
	Sep. 30, 2014
Regulatory Requirements [Abstract]	'
Regulatory Requirements	'
	13. Regulatory Requirements
	At September 30, 2014, aggregate excess regulatory capital for all of the Operating Companies was $ 3.25 billion.
	TH LLC and IB LLC are subject to the Uniform Net Capital Rule (Rule 15c3‑1) under the Exchange Act and the Commodities and Futures Trading Commission’s minimum financial requirements (Regulation 1.17), and THE is subject to the Swiss Financial Market Supervisory Authority eligible equity requirement. Additionally, THSHK is subject to the Hong Kong Securities Futures Commission liquid capital requirement, THA is subject to the Australian Stock Exchange liquid capital requirement,  THLI is subject to the Financial Market Authority Liechtenstein eligible capital requirements, THC and IBC are subject to the Investment Industry Regulatory Organization of Canada risk adjusted capital requirement, IBUK is subject to the U.K. Financial Conduct Authority  Capital Requirements Directive, IBI is subject to the National Stock Exchange of India net capital requirements and IBSJ is subject to the Japanese Financial Supervisory Agency capital requirements. The following table summarizes capital, capital requirements and excess regulatory capital, presented in millions.
		Net Capital/
		Eligible Equity		Requirement		Excess
	IB LLC	$	2,408.9	$	369.5	$	2,039.4
	TH LLC		334.3		65.7		268.6
	THE		693.4		210.5		482.9
	Other regulated Operating Companies		483.2		22.7		460.5
		$	3,919.8	$	668.4	$	3,251.4
	Regulatory capital requirements could restrict the Operating Companies from expanding their business and declaring dividends if their net capital does not meet regulatory requirements. Also, certain entities within the Company are subject to other regulatory restrictions and requirements.
	At September 30, 2014, all of the regulated Operating Companies were in compliance with their respective regulatory capital requirements.

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	14. Related Party Transactions
	Receivable from affiliate represents amounts advanced to Holdings and payable to affiliate represents amounts payable to Holdings under the Tax Receivable Agreement (see Note 4).
	Included in receivables from and payables to customers in the accompanying  condensed consolidated statements of financial condition as of September 30, 2014 and December 31, 2013 were accounts receivable from directors, officers and their affiliates of $5.3 million and $0.4 million and payables of $376.8 million and $815.5 million, respectively.

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Events	'
	15. Subsequent Events
	As required by FASB ASC Topic 855, “Subsequent Events”, the Company has evaluated subsequent events for adjustment to or disclosure in its condensed consolidated financial statements through the date the condensed consolidated financial statements were issued.
	No recordable or disclosable events, except as noted in Note 4, occurred.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2014
Significant Accounting Policies [Abstract]	'
Basis Of Presentation	'
	Basis of Presentation
	These condensed consolidated financial statements are presented in U.S. dollars and have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding financial reporting with respect to Form 10-Q.
	These condensed consolidated financial statements are unaudited and should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s 2013 Annual Report on Form 10-K for the year ended December 31, 2013, which was filed with the SEC on March 3, 2014. The condensed consolidated financial information as of December 31, 2013 has been derived from the audited consolidated financial statements not included herein.
	These unaudited condensed consolidated financial statements include the accounts of the Company and its consolidated subsidiaries and reflect all adjustments of a normal and recurring nature that are, in the opinion of management, necessary for the fair  presentation of the results for the interim periods presented.  The operating results for interim periods are not necessarily indicative of the operating results for the entire year.
Principles Of Consolidation, Including Noncontrolling Interests	'
	Principles of Consolidation, including Noncontrolling Interests
	These condensed consolidated financial statements include the accounts of IBG, Inc. and its majority and wholly owned subsidiaries.  As sole managing member of IBG LLC, IBG, Inc. exerts control over the IBG LLC’s operations. In accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810, “Consolidation”, the Company consolidates IBG LLC’s financial statements and records the interests in IBG LLC that it does not own as noncontrolling interests.
	The Company’s policy is to consolidate all other entities in which it owns more than 50% unless it does not have control. All inter‑company balances and transactions have been eliminated.
Use Of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in these condensed consolidated financial statements and accompanying notes. These estimates and assumptions are based on judgment and the best available information at the time. Therefore, actual results could differ materially from those estimates. Such estimates include the allowance for doubtful accounts, valuation of certain investments, compensation accruals, current and deferred income taxes, and estimated contingency reserves.
Fair Value	'
	Fair Value
	Substantially all of the Company’s assets and liabilities, including financial instruments are carried at fair value based on published market prices and are marked to market, or are assets and liabilities which are short‑term in nature and are carried at amounts that approximate fair value.
	The Company applies the fair value hierarchy in accordance with FASB ASC Topic 820, “Fair Value Measurement” (“ASC Topic 820”), to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets and liabilities and the lowest priority to unobservable inputs. The three levels of the fair value hierarchy are:
	Level 1	Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.
	Level 2	Quoted prices in markets that are not considered to be active or financial instruments for which all significant inputs are observable, either directly or indirectly.
	Level 3	Prices or valuations that require inputs that are both significant to fair value measurement and unobservable.
	Financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are generally classified as Level 1 of the fair value hierarchy. The Company’s Level 1 financial instruments, which are valued using quoted market prices as published by exchanges and clearing houses or otherwise broadly distributed in active markets, include active listed stocks, options, warrants and discount certificates, U.S. and foreign government securities and corporate and municipal bonds.  The Company does not adjust quoted prices for Level 1 financial instruments, even in the event that the Company may hold a large position whereby a purchase or sale could reasonably impact quoted prices.
	Currency forward contracts are valued using broadly distributed bank and broker prices, and are classified as Level 2 of the fair value hierarchy as such instruments are not exchange‑traded. Other securities that are not traded in active markets are also classified in Level 2 of the fair value hierarchy. Level 3 financial instruments are comprised of securities that have been delisted or otherwise are no longer tradable and have been valued by the Company based on internal estimates.
	Other fair value investments, included in other assets in the condensed consolidated statements of financial condition, are comprised of listed stocks, options, and corporate and municipal bonds that the Company does not carry in its market making business.  These investments are generally reported as Level 2 of the fair value hierarchy, except for unrestricted listed securities, which are classified as Level 1 of the fair value hierarchy, and delisted securities which are classified as Level 3 of the fair value hierarchy.  Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities in the condensed consolidated statements of financial condition, are comprised of unrestricted listed securities which are classified as Level 1 of the fair value hierarchy.
Earnings Per Share	'
	Earnings Per Share
	Earnings per share (“EPS”) are computed in accordance with FASB ASC Topic 260,  “Earnings per Share.”   Basic EPS is computed by dividing the net income available for common stockholders by the weighted average number of shares outstanding for that period. Diluted EPS is calculated by dividing the net income available for common stockholders by the diluted weighted average shares outstanding for that period. Diluted EPS includes the determinants of the basic EPS and, in addition, reflects the dilutive effect of shares of common stock estimated to be distributed in the future under the Company’s stock-based compensation plans, with no adjustments to net income available for common stockholders for dilutive potential common shares.
Stock-Based Compensation	'
	Stock‑Based Compensation
	The Company follows FASB ASC Topic 718, “Compensation - Stock Compensation” (“ASC Topic 718”), to account for its stock‑based compensation plans. ASC Topic 718 requires all share‑based payments to employees to be recognized in the condensed consolidated financial statements using a fair value‑based method. Grants, which are denominated in U.S. dollars, are communicated to employees in the year of grant, thereby establishing the fair value of each grant. The fair value of awards granted to employees are generally expensed as follows: 50% in the year of grant in recognition of plan forfeiture provisions (as described below) and the remaining 50% over the related vesting period utilizing the “graded vesting” method permitted under ASC Topic 718. In the case of “retirement eligible” employees (those employees older than 59), 100% of awards are expensed when granted.
	Awards granted under stock‑based compensation plans are subject to forfeiture in the event an employee ceases employment with the Company. The plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted.
Cash And Cash Equivalents	'
	Cash and Cash Equivalents
	The Company considers all highly liquid investments, with maturities of three months or less, that are not segregated and deposited for regulatory purposes or to meet margin requirements at clearing houses to be cash equivalents.
Cash And Securities - Segregated For Regulatory Purposes	'
	Cash and Securities - Segregated for Regulatory Purposes
	As a result of customer activities, certain Operating Companies are obligated by rules mandated by their primary regulators to segregate or set aside cash or qualified securities to satisfy such regulations, which regulations have been promulgated to protect customer assets. Securities segregated for regulatory purposes consisted of U.S. Treasury Bills of $4.58 billion and $1.30 billion at September 30, 2014 and December 31, 2013, respectively, and securities purchased under agreements to resell in the amount of $5.25 billion and $6.73 billion as of September 30, 2014 and December 31, 2013, respectively, which amounts approximate fair value.
Securities Borrowed And Securities Loaned	'
	Securities Borrowed and Securities Loaned
	Securities borrowed and securities loaned are recorded at the amount of the cash collateral advanced or received. Securities borrowed transactions require the Company to provide counterparties with collateral, which may be in the form of cash, letters of credit or other securities. With respect to securities loaned, the Company receives collateral, which may be in the form of cash or other securities in an amount generally in excess of the fair value of the securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as permitted contractually. The Company does not net, in the condensed consolidated statements of financial condition, securities borrowed and securities loaned entered into with the same counterparty.
	Securities lending fees received and paid by the Company are included in interest income or interest expense, respectively, in the condensed consolidated statements of comprehensive income.
Securities Purchased Under Agreements To Resell	'
	Securities Purchased Under Agreements to Resell
	Securities purchased under agreements to resell, which are reported as collateralized financing transactions, are recorded at contract value, plus accrued interest, which approximates fair value. To ensure that the fair value of the underlying collateral remains sufficient, the collateral is valued daily with additional collateral obtained or excess collateral returned, as permitted under contractual provisions. The Company does not net, in the condensed consolidated statements of financial condition, securities purchased under agreements to resell transactions and securities sold under agreements to repurchase transactions entered into with the same counterparty.
Financial Instruments Owned And Sold But Not Yet Purchased	'
	Financial Instruments Owned and Financial Instruments Sold, But Not Yet Purchased, at Fair Value
	Financial instrument transactions are accounted for on a trade date basis. Financial instruments owned and financial instruments sold, but not yet purchased are stated at fair value based upon quoted market prices. All firm‑owned financial instruments pledged to counterparties where the counterparty has the right, by contract or custom, to sell or repledge the financial instruments are reported as financial instruments owned and pledged as collateral in the condensed consolidated statements of financial condition.
	The Company also enters into currency forward contracts. These transactions, which are also accounted for on a trade date basis, are agreements to exchange a fixed amount of one currency for a specified amount of a second currency at completion of the currency forward contract term. Unrealized mark‑to‑market gains and losses on currency forward contracts are included in financial instruments owned, at fair value or financial instruments sold, but not yet purchased, at fair value in the condensed consolidated statements of financial condition.
Customer Receivables And Payables	'
	Customer Receivables and Payables
	Customer securities transactions are recorded on a settlement date basis and customer commodities transactions are recorded on a trade date basis. Receivables from and payables to customers include amounts due on cash and margin transactions, including futures contracts transacted on behalf of customers. Securities owned by customers, including those that collateralize margin loans or other similar transactions, are not reported in the condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are expensed and included in general and administrative expense in the condensed consolidated statements of comprehensive income.
Receivables From And Payables To Brokers, Dealers And Clearing Organizations	'
	Receivables from and Payables to Brokers, Dealers and Clearing Organizations
	Receivables and payables to brokers, dealers and clearing organizations include net receivables and payables from unsettled trades, including amounts related to futures and options on futures contracts executed on behalf of customers, amounts receivable for securities not delivered by the Company to the purchaser by the settlement date (“fails to deliver”) and cash margin deposits. Payables to brokers, dealers and clearing organizations also include amounts payable for securities not received by the Company from a seller by the settlement date (“fails to receive”).
Investments	'
	Investments
	The Company makes certain strategic investments related to its business and accounts for these investments under the cost method of accounting or under the equity method of accounting as required under FASB ASC Topic 323, “Investments—Equity Method and Joint Ventures.”   Investments accounted for under the equity method, including where the investee is a limited partnership or limited liability company, are recorded at the fair value amount of the Company’s initial investment and are adjusted each period for the Company’s share of the investee’s income or loss. The Company’s share of the income or losses from equity method investments is included in other income in the condensed consolidated statements of comprehensive income. The recorded amounts of the Company’s equity method investments, $34.7 million at September 30, 2014 ($27.5 million at December 31, 2013), which are included in other assets in the condensed consolidated statements of financial condition, increase or decrease accordingly. Contributions paid to and distributions received from equity method investees are recorded as additions or reductions, respectively, to the respective investment balance.
	The Company also holds exchange memberships and investments in equity securities of certain exchanges as required to qualify as a clearing member, and strategic investments in corporate stock that do not qualify for equity method accounting. Such investments, $30.1 million at September 30, 2014 ($27.6 million at December 31, 2013), are recorded at cost or, if an other‑than‑temporary impairment in value has occurred, at a value that reflects management’s estimate of the impairment, and are also included in other assets in the condensed consolidated statements of financial condition. Dividends received from cost basis investments are included in other income in the condensed consolidated statements of comprehensive income when such dividends are received.
	A judgmental aspect of accounting for investments is evaluating whether an other‑than‑temporary decline in the value of an investment has occurred. The evaluation of an other‑than‑temporary impairment is dependent on specific quantitative and qualitative factors and circumstances surrounding an investment, including recurring operating losses, credit defaults and subsequent rounds of financing.  The Company’s equity investments do not have readily determinable market values. All investments are reviewed for changes in circumstances or occurrence of events that suggest the Company’s investment may not be recoverable. If an unrealized loss on any investment is considered to be other‑than‑temporary, the loss is recognized in the period the determination is made
	The Company also has certain investments (which are not considered core business activities) that are accounted for at fair value (see Note 6) and included in other assets in the condensed consolidated statements of financial condition.  Gains and losses related to these investments are included in other income in the condensed consolidated statements of comprehensive income.
Property And Equipment	'
	Property and Equipment
	Property and equipment, which is included in other assets in the condensed consolidated statements of financial condition, consists of purchased technology hardware and software, internally developed software, leasehold improvements and office furniture and equipment. Property and equipment are recorded at historical cost, less accumulated depreciation and amortization. Additions and improvements that extend the lives of assets are capitalized, while expenditures for repairs and maintenance are expensed as incurred. Depreciation and amortization are computed using the straight‑line method. Equipment is depreciated over the estimated useful lives of the assets, while leasehold improvements are amortized over the lesser of the estimated economic useful life of the asset or the term of the lease. Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years.
Comprehensive Income And Foreign Currency Translation	'
	Comprehensive Income and Foreign Currency Translation
	The Company’s operating results are reported in the condensed consolidated statements of comprehensive income pursuant to FASB Accounting Standards Update 2011‑05, “Comprehensive Income”.
	Comprehensive income consists of two components: net income and other comprehensive income (“OCI”). OCI is comprised of revenues, expenses, gains and losses that are reported in the comprehensive income section of the statements of comprehensive income, but are excluded from reported net income. The Company’s OCI is comprised of foreign currency translation adjustments, net of related income taxes, where applicable. In general, the practice and intention of the Company is to reinvest the earnings of its non‑U.S. subsidiaries in those operations.
	The Company’s non‑U.S. domiciled subsidiaries have a functional currency that is other than the U.S. dollar. Such subsidiaries’ assets and liabilities are translated into U.S. dollars at period‑end exchange rates, and revenues and expenses are translated at average exchange rates prevailing during the period. Adjustments that result from translating amounts from a subsidiary’s functional currency to the U.S. dollar are reported net of tax, where applicable, in accumulated OCI in the condensed consolidated statements of financial condition.
Revenue Recognition	'
	Revenue Recognition
	—Trading Gains (Losses)
	Trading gains and losses are recorded on trade date and are reported on a net basis. Trading gains and losses are comprised of changes in the fair value of financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value (i.e., unrealized gains and losses) and realized gains and losses. Included in trading gains (losses) are net gains and losses on stocks, U.S. and foreign government securities, corporate and municipal bonds, options, futures, foreign exchange and other derivative instruments. Dividends are integral to the valuation of stocks and interest is integral to the valuation of fixed income instruments. Accordingly, both dividends and interest income and expense attributable to financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are reported on a net basis included in trading gains (losses) in the condensed consolidated statements of comprehensive income.
	—Commissions and Execution Fees
	Commissions charged for executing and clearing customer transactions are recorded on a trade date basis and are reported as commissions and execution fees and the related expenses are reported as execution and clearing expenses in the condensed consolidated statements of comprehensive income.
	—Interest Income and Expense
	The Company earns interest income and incurs interest expense primarily in connection with its electronic brokerage customer business and its securities lending activities, which are recorded on the accrual basis and are included in interest income and interest expense, respectively, in the condensed consolidated statements of comprehensive income.
	—Foreign Currency Transaction Gains and Losses
	Foreign currency transaction gains and losses from market making are included in trading gains (losses) in the condensed consolidated statements of comprehensive income. Electronic brokerage foreign currency transaction gains and losses are included in interest income (if arising from currency swap transactions) or other income in the condensed consolidated statements of comprehensive income.
Income Taxes	'
	Income Taxes
	The Company accounts for income taxes in accordance with FASB ASC Topic740, “Income Taxes” (“ASC Topic 740”). The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits are based on enacted tax laws (see Note 10) and reflect management’s best assessment of estimated future taxes to be paid. The Company is subject to income taxes in both the U.S. and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates.
	The Company recognizes interest related to income tax matters as interest income or expense and penalties related to income tax matters as income tax expense.
	Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statements recognition of the underlying assets and liabilities. In evaluating the ability to recover deferred tax assets within the jurisdictions from which they arise, the Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax‑planning strategies, and results of recent operations. In projecting future taxable income, historical results are adjusted for changes in accounting policies and incorporate assumptions including the amount of future state, federal and foreign pretax operating income, the reversal of temporary differences, and the implementation of feasible and prudent tax‑planning strategies. These assumptions require significant judgment about the forecasts of future taxable income and are consistent with the plans and estimates the Company is using to manage the underlying businesses. In evaluating the objective evidence that historical results provide, three years of cumulative operating income (loss) are considered. Deferred income taxes have not been provided for U.S. tax liabilities or for additional foreign taxes on the unremitted earnings of foreign subsidiaries that have been indefinitely reinvested.
	The calculation of the Company’s tax liabilities involves dealing with uncertainties in the application of complex tax laws and regulations in a multitude of jurisdictions across the Company’s global operations. Changes in tax laws and rates could also affect recorded deferred tax assets and liabilities in the future. The Company is not aware of any such changes that would have a material effect on the Company’s results of operations, cash flows, or financial position.
	ASC Topic 740 provides that a tax benefit from an uncertain tax position may be recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, on the basis of the technical merits. ASC Topic 740 also provides guidance on measurement, derecognition, classification, interest and penalties, accounting in interim periods, disclosure, and transition.
	The Company records tax liabilities in accordance with ASC Topic 740 and adjusts these liabilities when management’s judgment changes as a result of the evaluation of new information not previously available. Because of the complexity of some of these uncertainties, the ultimate resolution may result in payments that are different from the current estimates of these tax liabilities. These differences will be reflected as increases or decreases to income tax expense in the period in which new information becomes available.
Recently Issued Accounting Pronouncements	'
	Recently Issued Accounting Pronouncements
	Subsequent to the adoption of the ASC, the FASB will issue Accounting Standards Updates (“ASUs”) as the means to add to or delete from, or otherwise amend the ASC. In 2014, prior to the issuance of the Company’s condensed consolidated financial statements, ASUs 2013-05 through 2014-15 have been issued. Following is a summary of recently issued ASUs that have affected or may affect the Company’s condensed consolidated financial statements:
			Affects	Status
	ASU 2013-05		Foreign Currency Matters (Topic 830): Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity	Effective for fiscal periods beginning on or after December 15, 2013.
	ASU 2014-06		Technical Corrections and Improvements Related to Glossary Terms	Effective on issuance in March 2014.
	ASU 2014-09		Revenue from Contracts with Customers (Topic 606)	Effective for fiscal periods beginning on or after December 15, 2016
	ASU 2014-11		Transfers and Servicing (Topic 860): Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures.	Effective for the first interim or annual period beginning after December 15, 2014
	ASU 2014-12		Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period.	Effective for annual periods and interim periods within those annual periods beginning after December 15, 2015.
	ASU 2014-15		Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern	Effective for the first interim or annual period ending after December 15, 2016
	Adoption of those ASUs that became effective during 2014, prior to the issuance of the Company’s condensed consolidated financial statements, did not have a material effect on those financial statements

Equity_And_Earnings_Per_Share_

Equity And Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2014
Equity And Earnings Per Share [Abstract]	'
Earnings Per Share Basic And Diluted	'
	Earnings per Share
	Basic earnings per share are calculated utilizing net income available for common stockholders divided by the weighted average number of shares of Class A and Class B common stock outstanding for that period, presented in thousands, except shares and per share amounts:
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Basic earnings per share:
	Net income available for common stockholders	$	3,191	$	16,447	$	37,441	$	33,382
	Weighted average shares of common stock outstanding:
	Class A		57,098,952		49,965,950		55,956,515		48,807,221
	Class B		100		100		100		100
			57,099,052		49,966,050		55,956,615		48,807,321
	Basic earnings per share	$	0.06	$	0.33	$	0.67	$	0.68
	Diluted earnings per share are calculated utilizing the Company’s basic net income available for common stockholders divided by diluted weighted average shares outstanding with no adjustments to net income available to common stockholders for potentially dilutive common shares, presented in thousands, except shares and per share amounts:
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Diluted earnings per share:
	Net income available for common stockholders	$	3,191	$	16,447	$	37,441	$	33,382
	Weighted average shares of common stock outstanding:
	Class A:
	Issued and outstanding		57,098,952		49,965,950		55,956,515		48,807,221
	Potentially dilutive common shares issuable pursuant to employee incentive plans		1,121,018		1,022,164		1,239,498		1,174,343
	Class B		100		100		100		100
			58,220,070		50,988,214		57,196,113		49,981,664
	Diluted earnings per share	$	0.05	$	0.32	$	0.65	$	0.67

Comprehensive_Income_Tables

Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2014
Comprehensive Income Detail [Abstract]	'
Comprehensive Income Table	'
		Three months ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Comprehensive income (loss) available for common stockholders, net of tax	$	-7,594	$	20,077	$	28,502	$	29,666
	Earnings per share on comprehensive income:
	Basic	$	-0.13	$	0.40	$	0.51	$	0.61
	Diluted	$	-0.13	$	0.39	$	0.50	$	0.59
	Weighted average common shares outstanding:
	Basic		57,099,052		49,966,050		55,956,615		48,807,321
	Diluted		58,220,070		50,988,214		57,196,113		49,981,664

Financial_Assets_And_Financial1

Financial Assets And Financial Liabilities (Tables)	9 Months Ended
	Sep. 30, 2014
Financial Assets And Financial Liabilities [Abstract]	'
Fair Value Table	'
		Financial Assets At Fair Value as of September 30, 2014
		Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes	$	4,577,342		$	-		$	-		$	4,577,342
	Financial instruments owned:
	Stocks		836,551			-			106			836,657
	Options		1,255,124			-			-			1,255,124
	Warrants and discount certificates		44,099			-			-			44,099
	U.S. and foreign government securities		14,686			1,386			-			16,072
	Corporate and municipal bonds		68,735			11,565			-			80,300
	Currency forward contracts		-			4,601			-			4,601
	Total financial instruments owned		2,219,195			17,552			106			2,236,853
	Financial instruments owned and pledged as collateral:
	Stocks		1,070,314			-			-			1,070,314
	Warrants		307			-			-			307
	U.S. and foreign government securities		87,727			-			-			87,727
	Corporate and municipal bonds		975			-			-			975
	Total financial instruments owned and pledged as collateral		1,159,323			-			-			1,159,323
	Total financial instruments owned, at fair value		3,378,518			17,552			106			3,396,176
	Other fair value investments, included in other assets:
	Stocks and options		34,441			-			162			34,603
	Corporate and municipal bonds		-			1,567			-			1,567
	Total other fair value investments, included in other assets		34,441			1,567			162			36,170
	Total Financial Assets at Fair Value	$	7,990,301		$	19,119		$	268		$	8,009,688
		Financial Liabilities At Fair Value as of September 30, 2014
		Level 1			Level 2			Level 3			Total
	Financial instruments sold,  but not yet purchased, at fair value:
	Stocks	$	1,242,103		$	-		$	76		$	1,242,179
	Options		1,317,944			-			-			1,317,944
	Warrants and discount certificates		760			-			-			760
	U.S. and foreign government securities		-			1,648			-			1,648
	Corporate bonds		78,206			8,452			-			86,658
	Currency forward contracts		-			475			-			475
	Total financial instruments sold, but not yet purchased, at fair value		2,639,013			10,575			76			2,649,664
	Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities
	Stocks and options		64			-			-			64
	Total other fair value liabilities, included in accounts payable, accrued expenses and other liabilities		64			-			-			64
	Total Financial Liabilities at Fair Value	$	2,639,077		$	10,575		$	76		$	2,649,728
			Financial Assets At Fair Value as of December 31, 2013
			Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes		$	1,300,016		$	-		$	-		$	1,300,016
	Financial instruments owned:
	Stocks			1,243,914			-			57			1,243,971
	Options			1,880,481			-			-			1,880,481
	Warrants and discount certificates			57,144			-			-			57,144
	U.S. and foreign government securities			4,641			2,102			-			6,743
	Corporate and municipal bonds			72,750			18,476			-			91,226
	Currency forward contracts			-			5,748			-			5,748
	Total financial instruments owned			3,258,930			26,326			57			3,285,313
	Financial instruments owned and pledged as collateral:
	Stocks			1,097,734			-			-			1,097,734
	Warrants			233			-			-			233
	U.S. and foreign government securities			64,439			-			-			64,439
	Corporate and municipal bonds			1,125			-			-			1,125
	Total financial instruments owned and pledged as collateral			1,163,531			-			-			1,163,531
	Total financial instruments owned, at fair value			4,422,461			26,326			57			4,448,844
	Other fair value investments, included in other assets:
	Stocks			25,604			419			101			26,124
	Corporate and municipal bonds			1,776			47,896			-			49,672
	Mortgage backed securities			-			26,892			-			26,892
	Other asset backed securities			-			22,734			-			22,734
	Other			-			5,328			-			5,328
	Total other fair value investments, included in other assets			27,380			103,269			101			130,750
	Total Financial Assets at Fair Value		$	5,749,857		$	129,595		$	158		$	5,879,610
	Financial Liabilities At Fair Value as of December 31, 2013
	Level 1			Level 2			Level 3			Total
Financial instruments sold, but not yet purchased, at fair value:
Stocks	$	1,266,429		$	-		$	3		$	1,266,432
Options		1,793,248			-			-			1,793,248
Warrants and discount certificates		1,215			-			-			1,215
U.S. and foreign government securities		-			4,412			-			4,412
Corporate bonds		77,936			9,628			-			87,564
Currency forward contracts		-			802			-			802
Total financial instruments sold, but not yet purchased, at fair value	$	3,138,828		$	14,842		$	3		$	3,153,673
Level 3 Financial Assets And Financial Liabilities	'
		Financial Assets			Financial Liabilities
	Balance, January 1, 2014	$	158		$	3
	Total gains or losses (realized/unrealized)  - Included in earnings		99			-
	Purchases, issuances and settlements		-44			-
	Transfers in and/or out of Level 3		55			73
	Balance, September 30, 2014	$	268		$	76
		Financial Assets			Financial Liabilities
	Balance, January 1, 2013	$	-		$	-
	Total gains or losses (realized/unrealized) - Included in earnings		-184			77
	Purchases, issuances and settlements		-			-
	Transfers in and/or out of Level 3		365			-13
	Balance, September 30, 2013	$	181		$	64
Trading Gains From Market Making Transactions	'
		Three Months Ended						Nine months Ended
		September 30,						September 30,
		2014			2013			2014			2013
	Equities	$	44,731		$	65,562		$	196,440		$	227,078
	Fixed Income		5,706			4,449			17,797			18,920
	Foreign Exchange		-126,130			53,275			-78,398			-44,727
	Commodities		-			-			-			115
	Total Trading gains (losses)	$	-75,693		$	123,286		$	135,839		$	201,386
Netting Of Financial Assets And Financial Liabilities	'
		30-Sep-14
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
	Offsetting of Financial Assets:
	Securities segregated for regulatory purposes -purchased under agreements to resell	$	5,253.2	1		$	-		$	5,253.2		$	-5,253.20	$	-	$	-
	Securities borrowed		2,955.1				-			2,955.1			-2,868.10		-		87.0
	Securities purchased under agreements to resell		273.5				-			273.5			-273.5		-		-
	Financial Instruments owned, at fair value:		-										-
	Options		1,255.1				-			1,255.1			-1,206.30		-		48.8
	Warrants and discount certificates		44.4				-			44.4			-0.8		-		43.6
	Currency forward contracts		4.6				-			4.6			-		-		4.6
	Total	$	9,785.9			$	-		$	9,785.9		$	-9,601.90	$	-	$	184.0
									Net Amounts of			Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
	Offsetting of Financial Liabilities:
	Securities loaned	$	3,116.4			$	-		$	3,116.4		$	-3,114.50	$	-	$	1.9
	Financial instruments sold, but not yet purchased, at fair value:
	Options		1,318.0				-			1,318.0			-1,206.30		-		111.7
	Warrants and discount certificates		0.8				-			0.8			-0.8		-		-
	Currency forward contracts		0.5				-			0.5			-		-		0.5
	Total	$	4,435.7			$	-		$	4,435.7		$	-4,321.60	$	-	$	114.1
		31-Dec-13
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
	Offsetting of Financial Assets:
	Securities segregated for regulatory purposes - purchased under agreements to resell	$	6,734.2	1		$	-		$	6,734.2		$	-6,734.20	$	-	$	-
	Securities borrowed		2,751.5				-			2,751.5			-2,694.60		-		56.9
	Securities purchased under agreements to resell		386.3				-			386.3			-386.3		-		-
	Financial Instruments owned, at fair value:
	Options		1,880.5				-			1,880.5			-1,652.80		-		227.7
	Warrants and discount certificates		57.4				-			57.4			-1.2		-		56.2
	Currency forward contracts		5.7				-			5.7			-		-		5.7
	Total	$	11,815.6			$	-		$	11,815.6		$	-11,469.10	$	-	$	346.5
									Net Amounts of				Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
	Offsetting of Financial Liabilities:
	Securities loaned	$	2,563.7			$	-		$	2,563.7		$	-2,544.60	$	-	$	19.1
	Financial instruments sold, but not yet purchased, at fair value:
	Options		1,793.2				-			1,793.2			-1,652.80		-		140.4
	Warrants and discount certificates		1.2				-			1.2			-1.2		-		-
	Currency forward contracts		0.8				-			0.8			-		-		0.8
Total	$	4,358.9			$	-		$	4,358.9		$	-4,198.60	$	-	$	160.3
As of September 30, 2014 and December 31, 2013, the Company had $5.25 billion and $6.73 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in “Cash and securities—segregated for regulatory purposes” in the condensed consolidated statements of financial condition

Collateralized_Transactions_Ta

Collateralized Transactions (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure Collateralized Transactions [Abstract]	'
Amounts Related To Collateralized Transactions	'
			30-Sep-14				31-Dec-13
			Permitted		Sold or		Permitted		Sold or
			to Repledge		Repledged		to Repledge		Repledged
	Securities lending transactions		$	9,593.3	$	1,408.9	$	9,331.9	$	2,504.3
	Agreements to resell 1			5,527.5		5,524.2		7,116.1		7,099.6
	Customer margin assets			15,365.2		3,797.3		11,753.3		4,602.9
			$	30,486.0	$	10,730.4	$	28,201.3	$	14,206.8
		-1		At September 30, 2014, $5.25 billion or 95% (at December 31, 2013, $6.73 billion, or 95%) of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.
Financial Instruments Owned And Pledged Where The Counterparty Has The Right To Repledge	'
			September 30,		December 31,
			2014		2013
	Stocks		$	1,070.3	$	1,097.8
	Warrants			0.3		0.2
	U.S. and foreign government securities			87.7		64.4
	Corporate and municipal bonds			1.0		1.1
			$	1,159.3	$	1,163.5

Employee_Incentive_Plans_Table

Employee Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Employee Incentive Plans [Abstract]	'
Share Grants And Fair Value	'
			Fair Value at
			Date of Grant
		Shares	($ millions)
	In connection with IPO	927,943	$	27.8
	31-Jul-07	16,665		0.4
	31-Dec-07	1,055,206		32.9
	31-Dec-08	2,065,432		35.6
	31-Dec-09	2,448,031		42.8
	31-Dec-10	2,513,738		43.2
	31-Dec-11	3,411,613		50.8
	6-Jan-12	1,215,866		18.4
	31-Dec-12	3,629,960		50.5
	31-Dec-13	1,894,046		46.2
		19,178,500	$	348.6
2007 Stock Incentive Plan, ROI Summary	'
		Shares	Shares
		Stock	ROI Unit
		Incentive Plan	Stock Plan
	Balance, December 31, 2013	11,647,117	-
	Granted	-	-
	Forfeited 1	-507,858	15,518
	Distributed	-2,438,091	-2,496
	Balance, September 30, 2014	8,701,168	13,022
	ROI Unit Stock Plan number of forfeited shares related to prior years was adjusted by 15,518 shares during the period.

Segment_And_Geographic_Informa1

Segment And Geographic Information (Tables)	9 Months Ended
	Sep. 30, 2014
Segment And Geographic Information [Abstract]	'
Segment And Geographic Information	'
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Net revenues:
	Electronic brokerage	$	243.0	$	194.7	$	687.3	$	602.5
	Market making		-70.4		130.9		154.6		221.9
	Corporate and eliminations		-1.6		0.7		-6.7		1.9
	Total net revenues	$	171.0	$	326.3	$	835.2	$	826.3
	Income before income taxes:
	Electronic brokerage	$	152.4	$	108.4	$	418.1	$	342.7
	Market making		-111.8		87.5		22.8		66.1
	Corporate and eliminations		-1.1		0.5		-9.1		3.7
	Total income before income taxes	$	39.5	$	196.4	$	431.8	$	412.5
		September 30,		December 31,
		2014		2013
	Assets:
	Electronic brokerage	$	36,125.0	$	31,333.5
	Market making		11,910.7		12,139.5
	Corporate and eliminations		-6,427.50		-5,602.30
	Total assets	$	41,608.2	$	37,870.7
	The Company operates its automated global business in U.S. and international markets on more than 100 exchanges and market centers. A significant portion of the Company’s net revenues are generated by subsidiaries operating outside the U.S. International operations are comprised of electronic brokerage and market making activities in 24 countries in Europe, Asia and the Americas (outside the U.S.). The following table presents total net revenues and income before income taxes by geographic area for the three and nine months ended September 30, 2014 and 2013, presented in millions.
		Three Months Ended				Nine months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Net revenues:
	United States	$	123.2	$	265.4	$	658.5	$	597.3
	International		66.3		59.5		201.1		227.2
	Corporate and eliminations		-18.4		1.4		-24.3		1.8
	Total net revenues	$	171.1	$	326.3	$	835.3	$	826.3
	Income before income taxes:
	United States	$	29.9	$	180.9	$	392.0	$	331.9
	International		12.6		14.3		51.4		76.9
	Corporate and eliminations		-3		1.2		-11.6		3.7
	Total income before income taxes	$	39.5	$	196.4	$	431.8	$	412.5

Regulatory_Requirements_Tables

Regulatory Requirements (Tables)	9 Months Ended
	Sep. 30, 2014
Regulatory Requirements [Abstract]	'
Summary Of Capital, Capital Requirements And Excess Capital	'
		Net Capital/
		Eligible Equity		Requirement		Excess
	IB LLC	$	2,408.9	$	369.5	$	2,039.4
	TH LLC		334.3		65.7		268.6
	THE		693.4		210.5		482.9
	Other regulated Operating Companies		483.2		22.7		460.5
		$	3,919.8	$	668.4	$	3,251.4

Recovered_Sheet1

Organization and Nature of Business (Details)	9 Months Ended
	Sep. 30, 2014	Oct. 24, 2014	3-May-07
	segment
Organization And Nature Of Business [Abstract]	'	'	'
IBG Inc. ownership % of IBG LLC	14.10%	14.50%	10.00%
Number of operating segments	2	'	'

Significant_Accounting_Policie2

Significant Accounting Policies (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	3-May-07
Significant Accounting Policies [Abstract]	'	'	'
SIP expense - Year of grant	'	'	50.00%
SIP expense - Remaining vesting period	'	'	50.00%
SIP expense - Employees over 59 in year of grant	'	'	100.00%
Percent of shares forfeited post employment	'	'	50.00%
Over 59 percent of shares eligible	'	'	100.00%
U.S. Treasury Bills	$4,580,000,000	$1,300,000,000	'
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	5,250,000,000	6,730,000,000	'
Equity method investments	34,700,000	27,500,000	'
Cost method investments	$30,100,000	$27,600,000	'
Property and equipment useful lives	'Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years.	'	'

Equity_And_Earnings_Per_Share_1

Equity And Earnings Per Share (Narrative) (Details) (USD $)

0 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

36 Months Ended

89 Months Ended

Oct. 24, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2011

Dec. 31, 2010

Sep. 30, 2014

Sep. 30, 2014

Oct. 24, 2014

3-May-07

Equity And Earnings Per Share [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

IBG Inc. ownership % of IBG LLC

'

14.10%

'

'

14.10%

'

'

'

'

14.10%

14.10%

14.50%

10.00%

IBG Holdings ownership % of IBG LLC

'

85.90%

'

'

85.90%

'

'

'

'

85.90%

85.90%

85.50%

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

'

$277,900,000

'

'

$277,900,000

'

$294,700,000

'

'

$277,900,000

$277,900,000

'

'

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)B 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

'

'

'

'

Fair Value Of Issued Shares For Membership Exchange

'

'

'

'

'

'

'

'

'

'

'

35,200,000

'

Shares Issued

1,358,478

'

'

'

'

'

4,683,415

1,983,624

'

'

'

'

'

Thomas Peterffy and Affiliates Ownership

'

87.60%

'

'

87.60%

'

'

'

'

87.60%

87.60%

88.00%

84.60%

Dividends paid by IBG LLC

'

'

'

'

283,100,000

'

'

'

'

'

'

'

'

Cash dividend paid to IBG, Inc.

'

'

'

'

39,000,000

'

'

'

'

'

'

'

'

Dividends paid to common shareholders

'

$5,700,000

$5,700,000

$5,500,000

$16,886,000

$14,742,000

'

'

'

'

'

'

'

Declaration Date

'

'

'

'

21-Oct-14

'

'

'

'

'

'

'

'

Dividend per share

'

$0.10

$0.10

$0.10

$0.10

'

'

'

'

'

'

'

'

Payment Date

'

'

'

'

12-Dec-14

'

'

'

'

'

'

'

'

Record Date

'

'

'

'

1-Dec-14

'

'

'

'

'

'

'

'

Common Class A

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

57,247,149

'

'

57,247,149

'

54,788,049

'

'

57,247,149

57,247,149

'

'

Common stock, shares outstanding

'

57,104,682

'

'

57,104,682

'

54,664,095

'

'

57,104,682

57,104,682

'

'

Common Class B

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

'

Equity_And_Earnings_Per_Share_2

Equity And Earnings Per Share (Basic Table) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic earnings per share:	'	'	'	'
Net income available for common stockholders	$3,191	$16,447	$37,441	$33,382
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	57,099,052	49,966,050	55,956,615	48,807,321
Basic earnings per share	$0.06	$0.33	$0.67	$0.68
Common Class A	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	57,098,952	49,965,950	55,956,515	48,807,221
Common Class B	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	100	100	100	100

Equity_And_Earnings_Per_Share_3

Equity And Earnings Per Share (Diluted Table) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Diluted earnings per share:	'	'	'	'
Net income available for common stockholders	$3,191	$16,447	$37,441	$33,382
Weighted Average Shares Outstanding [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	57,099,052	49,966,050	55,956,615	48,807,321
Potentially dilutive common shares:	'	'	'	'
Issuable pursuant to 2007 ROI Unit Stock Plan	1,121,018	1,022,164	1,239,498	1,174,343
Weighted Average Number of Shares Outstanding, Diluted	58,220,070	50,988,214	57,196,113	49,981,664
Earnings Per Share, Diluted	$0.05	$0.32	$0.65	$0.67
Common Class A	'	'	'	'
Weighted Average Shares Outstanding [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	57,098,952	49,965,950	55,956,515	48,807,221
Common Class B	'	'	'	'
Weighted Average Shares Outstanding [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	100	100	100	100

Comprehensive_Income_Details

Comprehensive Income (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Comprehensive Income Detail [Abstract]	'	'	'	'
Comprehensive income (loss) available for common stockholders	($7,594)	$20,077	$28,502	$29,666
Earnings per share on comprehensive income:	'	'	'	'
Basic	($0.13)	$0.40	$0.51	$0.61
Diluted	($0.13)	$0.39	$0.50	$0.59
Weighted average common shares outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	57,099,052	49,966,050	55,956,615	48,807,321
Weighted Average Number of Shares Outstanding, Diluted	58,220,070	50,988,214	57,196,113	49,981,664

Financial_Assets_And_Financial2

Financial Assets And Financial Liabilities (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Transfers of financial instruments owned from level 1 to level 2	$1,700,000	$1,700,000	'
Transfers of financial instruments owned from level 2 to level 1	4,700,000	1,400,000	'
Transfers of financial instruments sold, but not yet purchased from level 1 to level 2	1,100,000	1,300,000	'
Transfers of financial instruments sold, but not yet purchased from level 2 to level 1	1,300,000	1,500,000	'
Transfers of Other Fair Value Investments From Level 1 to Level 2	1,500,000	'	'
Total financial assets, at fair value	8,009,688,000	'	5,879,610,000
Financial instruments sold, but not yet purchased, at fair value	2,649,664,000	'	3,153,673,000
Level 3	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Total financial assets, at fair value	268,000	'	158,000
Financial instruments sold, but not yet purchased, at fair value	$76,000	'	$3,000

Financial_Assets_And_Financial3

Financial Assets And Financial Liabilities (Fair Value Table) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities segregated for regulatory purposes	$4,577,342	$1,300,016
Financial instruments owned	2,236,853	3,285,313
Financial instruments owned and pledged as collateral	1,159,323	1,163,531
Total financial instruments owned, at fair value	3,396,176	4,448,844
Other fair value investments, included in other assets	36,170	130,750
Total Financial Assets at Fair Value	8,009,688	5,879,610
Financial instruments sold, but not yet purchased, at fair value	2,649,664	3,153,673
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	64	'
Total Financial Liabilities at Fair Value	2,649,728	'
Common Stock [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	836,657	1,243,971
Financial instruments owned and pledged as collateral	1,070,314	1,097,734
Other fair value investments, included in other assets	'	26,124
Financial instruments sold, but not yet purchased, at fair value	1,242,179	1,266,432
Stocks and options [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	34,603	'
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	64	'
Options owned [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	1,255,124	1,880,481
Financial instruments sold, but not yet purchased, at fair value	1,317,944	1,793,248
Warrants and discount certificates owned [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	44,099	57,144
Financial instruments sold, but not yet purchased, at fair value	760	1,215
Warrants [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned and pledged as collateral	307	233
U.S. And Foreign Government Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	16,072	6,743
Financial instruments owned and pledged as collateral	87,727	64,439
Financial instruments sold, but not yet purchased, at fair value	1,648	4,412
Corporate And Municipal Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	80,300	91,226
Financial instruments owned and pledged as collateral	975	1,125
Other fair value investments, included in other assets	1,567	49,672
Financial instruments sold, but not yet purchased, at fair value	86,658	87,564
Mortgage Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	26,892
Other Asset Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	22,734
Currency forward contracts owned [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	4,601	5,748
Financial instruments sold, but not yet purchased, at fair value	475	802
Other Assets - Investments [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	5,328
Level 1	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities segregated for regulatory purposes	4,577,342	1,300,016
Financial instruments owned	2,219,195	3,258,930
Financial instruments owned and pledged as collateral	1,159,323	1,163,531
Total financial instruments owned, at fair value	3,378,518	4,422,461
Other fair value investments, included in other assets	34,441	27,380
Total Financial Assets at Fair Value	7,990,301	5,749,857
Financial instruments sold, but not yet purchased, at fair value	2,639,013	3,138,828
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	64	'
Total Financial Liabilities at Fair Value	2,639,077	'
Level 1 | Common Stock [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	836,551	1,243,914
Financial instruments owned and pledged as collateral	1,070,314	1,097,734
Other fair value investments, included in other assets	'	25,604
Financial instruments sold, but not yet purchased, at fair value	1,242,103	1,266,429
Level 1 | Stocks and options [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	34,441	'
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	64	'
Level 1 | Options owned [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	1,255,124	1,880,481
Financial instruments sold, but not yet purchased, at fair value	1,317,944	1,793,248
Level 1 | Warrants and discount certificates owned [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	44,099	57,144
Financial instruments sold, but not yet purchased, at fair value	760	1,215
Level 1 | Warrants [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned and pledged as collateral	307	233
Level 1 | U.S. And Foreign Government Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	14,686	4,641
Financial instruments owned and pledged as collateral	87,727	64,439
Level 1 | Corporate And Municipal Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	68,735	72,750
Financial instruments owned and pledged as collateral	975	1,125
Other fair value investments, included in other assets	'	1,776
Financial instruments sold, but not yet purchased, at fair value	78,206	77,936
Level 2	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	17,552	26,326
Total financial instruments owned, at fair value	17,552	26,326
Other fair value investments, included in other assets	1,567	103,269
Total Financial Assets at Fair Value	19,119	129,595
Financial instruments sold, but not yet purchased, at fair value	10,575	14,842
Total Financial Liabilities at Fair Value	10,575	'
Level 2 | Common Stock [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	419
Level 2 | U.S. And Foreign Government Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	1,386	2,102
Financial instruments sold, but not yet purchased, at fair value	1,648	4,412
Level 2 | Corporate And Municipal Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	11,565	18,476
Other fair value investments, included in other assets	1,567	47,896
Financial instruments sold, but not yet purchased, at fair value	8,452	9,628
Level 2 | Mortgage Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	26,892
Level 2 | Other Asset Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	22,734
Level 2 | Currency forward contracts owned [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	4,601	5,748
Financial instruments sold, but not yet purchased, at fair value	475	802
Level 2 | Other Assets - Investments [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	'	5,328
Level 3	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	106	57
Total financial instruments owned, at fair value	106	57
Other fair value investments, included in other assets	162	101
Total Financial Assets at Fair Value	268	158
Financial instruments sold, but not yet purchased, at fair value	76	3
Total Financial Liabilities at Fair Value	76	'
Level 3 | Common Stock [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Financial instruments owned	106	57
Other fair value investments, included in other assets	'	101
Financial instruments sold, but not yet purchased, at fair value	76	3
Level 3 | Stocks and options [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Other fair value investments, included in other assets	$162	'

Financial_Assets_And_Financial4

Financial Assets And Financial Liabilities (Level 3 Financial Assets) (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Financial Assets Level 3 Rollforward [Abstract]	'	'
Beginning balance	$158	'
Total gains or losses (realized/unrealized) - Included in earnings (Assets)	99	-184
Purchases, issuances and settlements (Assets)	-44	'
Transfers in and/or out of Level 3 (Assets)	55	365
Ending balance	$268	$181

Financial_Assets_And_Financial5

Financial Assets And Financial Liabilities (Level 3 Financial Liabilities) (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Financial Liabilities Level 3 Rollforward [Abstract]	'	'
Beginning balance	$3	'
Total gains or losses (realized/unrealized) - Included in earnings (Liabilities)	'	77
Transfers in and/or out of Level 3 (Liabilities)	73	-13
Ending balance	$76	$64

Financial_Assets_And_Financial6

Financial Assets And Financial Liabilities (Trading Gains from Market Making Transactions) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financial Assets And Financial Liabilities [Abstract]	'	'	'	'
Equities	$44,731	$65,562	$196,440	$227,078
Fixed Income	5,706	4,449	17,797	18,920
Foreign Exchange	-126,130	53,275	-78,398	-44,727
Commodities	'	'	'	115
Trading gains	($75,693)	$123,286	$135,839	$201,386

Financial_Assets_And_Financial7

Financial Assets And Financial Liabilities (Netting of Financial Assets) (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	$9,785.90		$11,815.60
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	9,785.90		11,815.60
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-9,601.90		-11,469.10
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	184		346.5
Securities Segregated For Regulatory Purposes - Purchased Under Agreements To Resell [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	5,253.20	[1]	6,734.20	[1]
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	5,253.20		6,734.20
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-5,253.20		-6,734.20
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Securities Borrowed [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	2,955.10		2,751.50
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	2,955.10		2,751.50
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-2,868.10		-2,694.60
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	87		56.9
Securities Purchased Under Agreement to Resell [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	273.5		386.3
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	273.5		386.3
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-273.5		-386.3
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Options owned [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	1,255.10		1,880.50
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	1,255.10		1,880.50
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-1,206.30		-1,652.80
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	48.8		227.7
Warrants and discount certificates owned [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	44.4		57.4
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	44.4		57.4
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-0.8		-1.2
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	43.6		56.2
Currency forward contracts owned [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	4.6		5.7
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	4.6		5.7
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	0		0
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	$4.60		$5.70
[1]	As of September 30, 2014 and December 31, 2013, the Company had $5.25B billion and $6.73B billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in bCash and securitiesbsegregated for regulatory purposesb in the condensed consolidated statements of financial condition

Financial_Assets_And_Financial8

Financial Assets And Financial Liabilities (Netting of Financial Liabilities) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	$4,435.70	$4,358.90
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	4,435.70	4,358.90
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-4,321.60	-4,198.60
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	114.1	160.3
Securities Loaned [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	3,116.40	2,563.70
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	3,116.40	2,563.70
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-3,114.50	-2,544.60
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	1.9	19.1
Options Sold, Not Yet Purchased [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	1,318	1,793.20
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	1,318	1,793.20
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-1,206.30	-1,652.80
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	111.7	140.4
Warrants And Discount Certificates Sold, Not Yet Purchased [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	0.8	1.2
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	0.8	1.2
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-0.8	-1.2
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	0	0
Currency Forward Contracts Sold, Not Yet Purchased [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	0.5	0.8
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	0.5	0.8
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	0	0
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	$0.50	$0.80

Collateralized_Transactions_Na

Collateralized Transactions (Narrative) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Disclosure Collateralized Transactions [Abstract]	'	'
Customer margin loans outstanding	$17,261,440,000	$13,596,650,000
Securities repledged and deposited for customers	$5,250,000,000	$6,730,000,000
Percentage of securities repledged and deposited for customers	95.00%	95.00%

Collateralized_Transactions_Am

Collateralized Transactions (Amounts Related to Collateralized Transactions) (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Permitted To Repledge [Member]	'		'
Collateralized Transactions [Line Items]	'		'
Securities lending transactions	$9,593.30		$9,331.90
Agreements to resell	5,527.50	[1]	7,116.10	[1]
Customer margin assets	15,365.20		11,753.30
Total collateralized transactions	30,486		28,201.30
Sold Or Repledged [Member]	'		'
Collateralized Transactions [Line Items]	'		'
Securities lending transactions	1,408.90		2,504.30
Agreements to resell	5,524.20	[1]	7,099.60	[1]
Customer margin assets	3,797.30		4,602.90
Total collateralized transactions	$10,730.40		$14,206.80
[1]	At September 30, 2014, $5.25 billion or 95% (at December 31, 2013, $6.73 billion, or 95%) of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.

Collateralized_Transactions_Fi

Collateralized Transactions (Financial instruments owned and pledged where the counterparty has the right to repledge) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Disclosure Collateralized Transactions [Abstract]	'	'
Stocks	$1,070.30	$1,097.80
Warrants	0.3	0.2
U.S. and foreign government securities	87.7	64.4
Corporate and municipal bonds	1	1.1
Financial Instruments Owned and Pledged as Collateral - Eligible to be Repledged by Counterparty	$1,159.30	$1,163.50

Senior_Secured_Revolving_Credi1

Senior Secured Revolving Credit Facility (Details) (USD $)	Aug. 08, 2014
In Millions, unless otherwise specified
Senior Secured Revolving Credit Facility [Abstract]	'
Senior secured revolving credit facility maximum capacity	$100

Employee_Incentive_Plans_Narra

Employee Incentive Plans (Narrative) (Details) (USD $)	0 Months Ended	9 Months Ended		89 Months Ended
In Millions, except Share data, unless otherwise specified	3-May-07	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Apr. 24, 2014	Dec. 31, 2013	3-May-07	Dec. 31, 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'
ROI Dollar Unit Payable	'	$3.10	'	$3.10	'	$5.60	'	'
Vested balance of ROI payable	'	3.1	'	3.1	'	5.6	'	'
ROI dollar compensation expense	'	0.2	0.5	'	'	'	'	'
Common Stock Shares issued under ROI Unit Stock Plan	'	'	'	'	'	'	1,271,009	'
ROI Shares issued to IBG LLC	'	'	'	'	'	'	1,250,000	'
2007 SIP shares issued under ROI Unit Stock Plan	'	'	'	'	'	'	21,009	'
Fair value ROI Treasury Stock	'	'	'	'	'	'	38.1	'
Fair Value ROI Accrual	'	'	'	'	'	'	'	17.8
Maximum shares of stock distributable under 2007 Stock Incentive Plan	'	30,000,000	'	30,000,000	'	20,000,000	'	'
Increase in 2007 Stock Incentive Plan shares	'	'	'	'	10,000,000	'	'	'
Shares granted to external directors	'	'	'	20,423	'	'	'	'
2007 Stock Incentive Plan Compensation Expense	'	31.5	28.1	'	'	'	'	'
Estimated Future 2007 Stock Incentive Plan Compensation Expense	'	$26.40	'	$26.40	'	'	'	'
Percent Shares Forfeited Post Employment	'	'	'	'	'	'	50.00%	'
Over Fifty Nine Percent Unvested Shares Eligible	'	'	'	'	'	'	100.00%	'
Former employees vesting schedule (Years)	'5 years	'	'	'	'	'	'	'
Post employment vesting percentage (Years 1 - 4)	'	'	'	'	'	'	12.50%	'
Post employment vesting percentage (Year 5)	'	'	'	'	'	'	50.00%	'
Post employment shares distribution	'	'	'	179,246	'	'	'	'
2007 ROI Unit Stock Plan [Member]	'	'	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'
Vesting Percentage	'	'b" 10% on the date of the IPO (or on the first anniversary of the IPO, in the case of U.S. ROI Unit holders who made the above-referenced elections after DecemberB 31, 2006); andb" an additional 15% on each of the first six anniversaries of the date of the IPO, assuming continued employment with the Company and compliance with other applicable covenants.	'	'	'	'	'	'
2007 Stock Incentive Plan (Shares)	'	'	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'
Vesting Percentage	'	'b" 10% on the first vesting date, which approximates the anniversary of the IPO; andb" an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with the Company and compliance with non-competition and other applicable covenants.	'	'	'	'	'	'

Employee_Incentive_Plans_Share

Employee Incentive Plans (Share Grants And Fair Value) (Details) (USD $)	89 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 06, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Jul. 31, 2007	3-May-07
Employee Incentive Plans [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Shares granted	'	1,894,046	3,629,960	1,215,866	3,411,613	2,513,738	2,448,031	2,065,432	1,055,206	16,665	927,943
Fair Value - Date of Grant ($000's)	'	$46.20	$50.50	$18.40	$50.80	$43.20	$42.80	$35.60	$32.90	$0.40	$27.80
Shares Granted IPO to Date	19,178,500	'	'	'	'	'	'	'	'	'	'
Fair Value - Date of Grant ($000's) IPO to Date	$348.60	'	'	'	'	'	'	'	'	'	'

Employee_Incentive_Plans_2007_

Employee Incentive Plans (2007 Stock Incentive Plan, ROI Summary) (Details)	9 Months Ended
	Sep. 30, 2014
2007 Stock Incentive Plan (Shares)	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Beginning Balance	11,647,117
Shares Forfeited	-507,858
Shares Distributed	-2,438,091	[1]
Ending Balance	8,701,168
Return On Investment Dollar Units [member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Beginning Balance	'
Shares Granted	'
Shares Forfeited	15,518
Shares Distributed	-2,496	[1]
Ending Balance	13,022
[1]	ROI Unit Stock Plan number of forfeited shares related to prior years was adjusted by 15,518 shares during the period.

Income_Taxes_Details

Income Taxes (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Income Taxes [Abstract]	'	'
Undistributed accumulated earnings of foreign subsidiaries	$1,091.10	$1,072.90
Accumulated earnings of foreign pass through subsidiaries	414	422.3
Accumulated earnings subject to additional foreign tax	$309	$318.70

Recovered_Sheet2

Commitments, Contingencies and Guarantees (Details) (USD $)	1 Months Ended	12 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Sep. 30, 2014	Sep. 30, 2014
			Scenario, Forecast [Member]
Commitment And Contingencies [Line Items]	'	'	'
Percentage of loss on securities	90.00%	'	'
Loss on large positions on Singapore Exchange	$64	$82	$84

Segment_And_Geographic_Informa2

Segment And Geographic Information (Segment Table) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	$170,974	$326,252	$835,181	$826,282	'
Income before income taxes	39,381	196,382	431,734	412,531	'
Assets	41,608,206	'	41,608,206	'	37,870,700
Electronic Brokerage [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	243,000	194,700	687,300	602,500	'
Income before income taxes	152,400	108,400	418,100	342,700	'
Assets	36,125,000	'	36,125,000	'	31,333,500
Market Making [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	-70,400	130,900	154,600	221,900	'
Income before income taxes	-111,800	87,500	22,800	66,100	'
Assets	11,910,700	'	11,910,700	'	12,139,500
Corporate And Eliminations [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	-1,600	700	-6,700	1,900	'
Income before income taxes	-1,100	500	-9,100	3,700	'
Assets	($6,427,500)	'	($6,427,500)	'	($5,602,300)

Segment_And_Geographic_Informa3

Segment And Geographic Information (Geographic Table) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	$170,974	$326,252	$835,181	$826,282
Income before income taxes	39,381	196,382	431,734	412,531
United States [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	123,200	265,400	658,500	597,300
Income before income taxes	29,900	180,900	392,000	331,900
International [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	66,300	59,500	201,100	227,200
Income before income taxes	12,600	14,300	51,400	76,900
Corporate And Eliminations [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	-18,400	1,400	-24,300	1,800
Income before income taxes	($3,000)	$1,200	($11,600)	$3,700

Regulatory_Requirements_Narrat

Regulatory Requirements (Narrative) (Details) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Regulatory Requirements [Abstract]	'
Excess regulatory capital	$3,251.40

Regulatory_Requirements_Summar

Regulatory Requirements (Summary Of Capital, Capital Requirements And Excess Capital) (Details) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Net Capital / Eligible Equity	$3,919.80
Required net capital	668.4
Excess regulatory capital	3,251.40
IB LLC [Member]	'
Net Capital / Eligible Equity	2,408.90
Required net capital	369.5
Excess regulatory capital	2,039.40
TH LLC [Member]	'
Net Capital / Eligible Equity	334.3
Required net capital	65.7
Excess regulatory capital	268.6
THE [Member]	'
Net Capital / Eligible Equity	693.4
Required net capital	210.5
Excess regulatory capital	482.9
Other Regulated Operating Companies [Member]	'
Net Capital / Eligible Equity	483.2
Required net capital	22.7
Excess regulatory capital	$460.50

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Related Party Transactions [Abstract]	'	'
Due from Related Parties - Customers	$5.30	$0.40
Due to Related Parties - Customers	$376.80	$815.50