Interactive Brokers (IBKR) 10-Q/A12 Nov 132013 FY Quarterly report (amended)Financial data

Company Profile

Documentation_and_Entity_Infor

Documentation and Entity Information	3 Months Ended
	Sep. 30, 2013	Nov. 08, 2013	Nov. 08, 2013
	Sep. 30, 2013	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-13	'	'
Amendment Flag	'false	'	'
Fiscal Year Focus	'2013	'	'
Fiscal Period Focus	'FY	'	'
Current Fiscal Year End Date	'--12-31	'	'
Well Known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Current Reporting Status	'Yes	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Common Stock Shares Outstanding	'	49,971,727	100

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Financial Condition (Unaudited) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets	'	'
Cash and cash equivalents	$1,548,520	$1,614,592
Cash and securities - segregated for regulatory purposes	12,681,070	12,482,388
Securities borrowed	3,363,242	2,833,145
Securities purchased under agreements to resell	487,774	428,904
Financial instruments owned, at fair value:	'	'
Financial instruments owned	3,454,897	3,617,879
Financial instruments owned and pledged as collateral	970,376	926,857
Total financial instruments owned	4,425,273	4,544,736
Receivables:	'	'
Customers, less allowance for doubtful accounts of $3,540 and $1,416 at September 30, 2013 and December 31, 2012	12,727,552	9,851,018
Receivables from brokers, dealers and clearing organizations	490,859	844,584
Receivable from affiliate	651	620
Interest receivable	24,236	22,829
Total receivables	13,243,298	10,719,051
Other assets	527,867	576,741
Total assets	36,277,044	33,199,557
Liabilities and equity	'	'
Financial instruments sold but not yet purchased, at fair value	3,593,292	4,286,260
Securities loaned	2,193,008	1,839,274
Short-term borrowings	2,579	110,420
Payables:	'	'
Customers	24,809,349	21,421,978
Payables to brokers, dealers and clearing organizations	234,833	361,834
Payable to affiliate	259,723	259,441
Accounts payable, accrued expenses and other liabilities	108,895	102,695
Interest payable	2,483	4,508
Total payables	25,415,283	22,150,456
Total liabilities	31,204,162	28,386,410
Stockholders' equity:	'	'
Common stock	501	478
Additional paid-in capital	517,865	493,912
Retained earnings	100,712	82,072
Accumulated other comprehensive income, net of income taxes of $1,081 and $1,417 at September 30, 2013 and December 31, 2012	26,038	29,754
Treasury stock, at cost, 124,835 and 298,105 shares at September 30, 2013 and December 31, 2012	-2,518	-7,718
Total stockholders' equity	642,598	598,498
Noncontrolling interests	4,430,284	4,214,649
Total equity	5,072,882	4,813,147
Total liabilities and stockholders' equity	36,277,044	33,199,557
Common Class A	'	'
Stockholders' equity:	'	'
Common stock	501	478
Common Class B	'	'
Stockholders' equity:	'	'
Common stock	$0	$0

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Financial Condition (Parenthetical) (Unaudited) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Allowance for doubtful accounts	$3,540	$1,416
Accumulated Other Comprehensive Income, Tax	$1,081	$1,417
Treasury stock shares	124,835	298,105
Common Class A	'	'
Common stock, par value	$0.01	$0.01
Shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	50,096,562	47,797,844
Common stock, shares outstanding	49,971,727	47,499,739
Common Class B	'	'
Common stock, par value	$0.01	$0.01
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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:	'	'	'	'
Trading gains	$123,286	$149,700	$201,386	$371,987
Commissions and execution fees	120,331	100,584	377,961	309,540
Interest income	74,000	65,410	220,572	200,607
Other income	20,826	17,104	64,999	50,750
Total revenues	338,443	332,798	864,918	932,884
Interest expense	12,191	14,199	38,636	49,475
Total net revenues	326,252	318,599	826,282	883,409
Non-interest expenses:	'	'	'	'
Execution and clearing	56,016	61,646	180,283	192,441
Employee compensation and benefits	44,242	57,676	148,578	180,202
Occupancy, depreciation and amortization	9,387	9,043	28,705	28,934
Communications	6,125	6,089	17,281	17,249
General and administrative	14,100	11,525	38,904	33,779
Total non-interest expenses	129,870	145,979	413,751	452,605
Income before income taxes	196,382	172,620	412,531	430,804
Income tax expense	10,414	14,747	31,239	34,458
Net income	185,968	157,873	381,292	396,346
Less net income attributable to noncontrolling interests	169,521	145,385	347,910	364,790
Net income attributable to common stockholders	16,447	12,488	33,382	31,556
Earnings per share:	'	'	'	'
Basic	$0.33	$0.26	$0.68	$0.70
Diluted	$0.32	$0.26	$0.67	$0.70
Weighted average common shares outstanding:	'	'	'	'
Basic	49,966,050	47,488,459	48,807,321	46,588,213
Diluted	50,988,214	47,679,818	49,981,664	46,865,770
Comprehensive income:	'	'	'	'
Net income attributable to common stockholders	16,447	12,488	33,382	31,556
Other comprehensive income:	'	'	'	'
Cumulative translation adjustment, before income taxes	3,691	2,965	-4,051	1,274
Income taxes related to items of other comprehensive income	61	1,071	-335	460
Other comprehensive income (loss), net of tax	3,630	1,894	-3,716	814
Comprehensive income attributable to common stockholders	20,077	14,382	29,666	32,370
Comprehensive income attributable to noncontrolling interests:	'	'	'	'
Net income attributable to noncontrolling interests	169,521	145,385	347,910	364,790
Other comprehensive income (loss) - cumulative translation adjustment	26,013	21,934	-29,602	9,876
Comprehensive income attributable to noncontrolling interests	$195,534	$167,319	$318,308	$374,666

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:	'	'
Net income	$381,292	$396,346
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Translation losses (gains)	19,839	-678
Deferred income taxes	11,164	16,881
Depreciation and amortization	13,914	14,201
Employee stock plan compensation	28,086	54,032
(Gains) losses on other investments, net	-2,728	7,742
Bad debt expense and other	2,472	607
Change in operating assets and liabilities:	'	'
Increase in cash and securities - segregated for regulatory purposes	-199,142	-2,255,850
Increase in securities borrowed	-530,221	-303,477
(Increase) decrease in securities purchased under agreements to resell	-58,852	31,218
Decrease in financial instruments owned	110,268	911,667
Increase in receivables from customers	-2,876,532	-2,367,432
Decrease in other receivables	350,520	523,193
Decrease (increase) in other assets	23,258	-5,900
Decrease in financial instruments sold but not yet purchased	-695,806	-1,606,918
Increase in securities loaned	354,398	559,452
Increase in payable to customers	3,387,375	3,978,476
(Decrease) increase in other payables	-127,152	258,159
Net cash provided by operating activities	192,153	211,719
Cash flows from investing activities:	'	'
Purchases of other investments	-189,934	-326,784
Proceeds from sales of other investments	202,245	292,826
Distributions received from and redemptions of equity investments	11,054	1,567
Purchase of property and equipment	-12,006	-13,971
Net cash provided by (used in) investing activities	11,359	-46,362
Cash flows from financing activities:	'	'
Dividends paid to noncontrolling interests	-107,698	-105,264
Redemptions of senior notes	0	-101,411
(Decrease) increase in short-term borrowings, net	-110,566	10,008
Net cash used in financing activities	-233,006	-210,722
Effect of exchange rate changes on cash and cash equivalents	-36,578	9,375
Net decrease in cash and cash equivalents	-66,072	-35,990
Cash and cash equivalents at beginning of period	1,614,592	1,695,495
Cash and cash equivalents at end of period	1,548,520	1,659,505
Supplemental disclosures of cash flow information:	'	'
Cash paid for interest	40,661	51,168
Cash paid for taxes	45,243	25,352
Non-cash financing activities:	'	'
Adjustments to additional paid-in capital for changes in proportionate ownership in IBG LLC	20,463	13,766
Adjustments to noncontrolling interests for changes in proportionate ownership in IBG LLC	-20,463	-13,766
Changes in redemption value of redeemable noncontrolling interests	0	-5,269,619
Changes to total equity (deficit) for the change in the redemption value of redeemable noncontrolling interests	$0	$5,269,619

Condensed_Consolidated_Stateme4

Condensed Consolidated Statements of Changes in Equity (Unaudited) (USD $)	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income	Total Stockholders' Equity (Deficit)	Other Noncontrolling Interests	Redeemable Noncontrolling Interests
In Thousands, except Share data	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income	Total Stockholders' Equity (Deficit)	Other Noncontrolling Interests	Redeemable Noncontrolling Interests
Balance at Dec. 31, 2011	($457,664)	$460	$0	($13,310)	($465,138)	$18,487	($459,501)	$1,837	$5,269,619
Common stock, shares issued at Dec. 31, 2011	'	46,061,256	'	'	'	'	'	'	'
Adjustment of redeemable noncontrlling interests from temporary to permanent equity (Note 4)	5,367,553	'	472,409	'	572,840	'	1,045,249	4,322,304	-5,269,619
Common stock distributed pursuant to stock plans	5,526	17	-17	5,526	'	'	5,526	'	'
Common Stock distributed pursuant to stock plans (in shares)	'	1,727,973	'	'	'	'	'	'	'
Compensation for stock grants vesting in the future	24,021	'	5,759	'	'	'	5,759	18,262	'
Deferred tax benefit retained	495	'	495	'	'	'	495	'	'
Dividends paid to shareholders	-14,055	'	'	'	-14,055	'	-14,055	'	'
Dividends paid by IBG LLC to other noncontrolling interests	-70,271	'	'	'	'	'	0	-70,271	'
Adjustments for changes in proportionate ownership in IBG LLC	13,741	'	13,766	'	'	'	13,766	-25	'
Comprehensive Income, net of tax	285,496	'	'	'	31,556	814	32,370	253,126	'
Balance at Sep. 30, 2012	5,154,842	477	492,412	-7,784	125,203	19,301	629,609	4,525,233	0
Common stock, shares issued at Sep. 30, 2012	'	47,789,229	'	'	'	'	'	'	'
Balance at Dec. 31, 2012	4,813,147	478	493,912	-7,718	80,072	29,754	598,498	4,214,649	'
Common stock, shares issued at Dec. 31, 2012	'	47,797,844	'	'	'	'	'	'	'
Common stock distributed pursuant to stock plans	5,200	23	-23	5,200	'	'	5,200	'	'
Common Stock distributed pursuant to stock plans (in shares)	'	2,298,718	'	'	'	'	'	'	'
Compensation for stock grants vesting in the future	29,001	'	3,513	'	'	'	3,513	25,488	'
Dividends paid to shareholders	-14,742	'	'	'	-14,742	'	-14,742	'	'
Dividends paid by IBG LLC to other noncontrolling interests	-107,698	'	'	'	'	'	0	-107,463	'
Adjustments for changes in proportionate ownership in IBG LLC	0	'	20,463	'	'	'	20,463	-20,463	'
Comprehensive Income, net of tax	347,974	'	'	'	33,382	-3,716	29,666	318,308	'
Balance at Sep. 30, 2013	$5,072,882	$501	$517,865	($2,518)	$100,712	$26,038	$642,598	$4,430,284	'
Balance (in shares) at Sep. 30, 2013	'	50,096,562	'	'	'	'	'	'	'

Organization_and_Nature_Of_Bus

Organization and Nature Of Business	3 Months Ended
Organization and Nature Of Business	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Organization and nature of business	'
	1. Organization and Nature of Business

	Interactive Brokers Group, Inc. (“IBG, Inc.” or the “Company”) is a Delaware holding company whose primary asset is its ownership of approximately 12.4% of the membership interests of IBG LLC, which, in turn, owns operating subsidiaries (collectively, “IBG LLC” or the “Group”). The accompanying unaudited condensed consolidated financial statements of IBG, Inc. reflect the consolidation of IBG, Inc.’s investment in IBG LLC for all periods presented (Note 4). IBG LLC is an automated global electronic broker and market maker specializing in routing orders and processing trades in securities, futures and foreign exchange instruments.

	IBG LLC is a Connecticut limited liability company that conducts its business through its operating subsidiaries (collectively called the “Operating Companies”): Timber Hill LLC (“TH LLC”), Timber Hill Europe AG (“THE”), Timber Hill Securities Hong Kong Limited (“THSHK”), Timber Hill Australia Pty Limited (“THA”), Timber Hill Canada Company (“THC”), Interactive Brokers LLC (“IB LLC”) and subsidiary, Interactive Brokers Canada Inc. (“IBC”), Interactive Brokers (U.K.) Limited (“IBUK”), Interactive Brokers (India) Private Limited (“IBI”), Interactive Brokers Financial Products S.A. (“IBFP”), Interactive Brokers Hungary KFT (“IBH”), IB Exchange Corp. (“IBEC”), Interactive Brokers Securities Japan, Inc. (“IBSJ”), IB Brasil Participações Ltda (“IBBH”), Interactive Brokers Software Services Estonia OU (“IBEST”) and Interactive Brokers Software Services Russia (“IBRUS”).

	IBG, Inc. operates in two business segments, electronic brokerage and market making. IBG, Inc. 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 (Note 14). 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	3 Months Ended
	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Significant Accounting Policies	'
	2. Significant Accounting Policies

	Basis of Presentation

	These unaudited condensed consolidated financial statements are presented in U.S. dollars and have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding financial reporting with respect to Form 10-Q and accounting standards generally accepted in the United States of America (“U.S. GAAP”) promulgated in the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC” or the “Codification”). These unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries and include all adjustments of a normal, recurring nature necessary to present fairly the financial condition as of September 30, 2013 and December 31, 2012, the results of operations and comprehensive income for the three and nine months ended September 30, 2013 and 2012 and cash flows for the nine months ended September 30, 2013 and 2012. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in IBG, Inc.’s 2012 Annual Report on Form 10-K filed with the SEC on March 8, 2013. The condensed consolidated financial statement information as of December 31, 2012 has been derived from the 2012 audited consolidated financial statements. The results of operations for interim periods are not necessarily indicative of results for the entire year.

	Principles of Consolidation, including Noncontrolling Interests

	The unaudited 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 Group’s operations. In accordance with ASC 810, Consolidation, the Company consolidates the Group’s consolidated financial statements and records the interests in the Group that IBG, Inc. does not own as noncontrolling interests. Prior to the June 6, 2012 amendment (the “Amendment”) to the Exchange Agreement (Note 4), the Company was required to report IBG Holdings LLC’s (“Holdings”) ownership as redeemable noncontrolling interests (i.e., temporary equity) pursuant to ASC 810-10-45, ASC 815-40-25 and ASC 480-10-S99-3A (formerly FASB Emerging Issues Task Force Topic D-98), outside of total equity. Redemption value of these redeemable noncontrolling interests was measured as the number of equivalent shares of member interests in IBG LLC owned by Holdings multiplied by the then current market price per share of the Company’s common stock. The excess of the redemption value over the book value of these interests, which did not affect net income attributable to common stockholders or cash flows, was required to be accounted for as a reduction of the Company’s stockholders’ equity.

	The Company elected to recognize changes in redemption value in each reporting period immediately as they occurred as if the end of each reporting period was also the redemption date for the entire redeemable noncontrolling interest under paragraph 15(b) of ASC 480-10-S99-3A, notwithstanding that the redeemable noncontrolling interests are redeemable over a period of time pursuant to a redemption schedule (Note 4).

	For periods after the above referenced amendment, the noncontrolling interests in IBG LLC attributable to Holdings are reported as a component of equity.

	The Company’s policy is to consolidate all entities of which it owns more than 50% unless it does not have control. All inter-company balances and transactions have been eliminated. IBG, Inc. would also consolidate any Variable Interest Entities (“VIEs”) pursuant to ASC 860, Transfers and Servicing and ASC 810 of which it is the primary beneficiary. IBG, Inc. currently is not the primary beneficiary of any such entities and therefore no VIEs are included in the unaudited condensed consolidated financial statements.

	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 the unaudited condensed consolidated financial statements and accompanying notes. Estimates, by their nature, are based on judgment and available information. Therefore, actual results could differ materially from those estimates. Such estimates include the estimated fair values of IBG LLC and the Company in connection with accounting for redeemable noncontrolling interests, the estimated value of investments accounted for under the equity method of accounting, the estimated useful lives of property and equipment, including capitalized internally developed software, the allowance for doubtful accounts, compensation accruals, current and deferred income taxes and estimated contingency reserves.

	Fair Value

	At September 30, 2013 and December 31, 2012, substantially all of IBG, Inc.’s assets and liabilities, including financial instruments, were carried at fair value based on published market prices and were marked to market, or were assets which are short-term in nature and were carried at amounts that approximate fair value.

	IBG, Inc. applies the fair value hierarchy of ASC 820, Fair Value Measurement, 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; and
	Level 3	Prices or valuations that require inputs that are both significant to fair value measurement and unobservable.

	Financial instruments owned and financial instruments sold, but not yet purchased are generally classified as Level 1 financial instruments. 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 U.S. government and sovereign obligations, active listed securities, options, futures, options on futures and corporate and municipal debt securities. IBG, Inc. 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 financial instruments as such instruments are not exchange-traded. Other securities that are not traded in active markets are also classified in Level 2. 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, excluding securities subject to corporate actions that have a determinable external price, which remain classified as Level 1 securities.

	Other fair value investments, reported in other assets in the accompanying unaudited condensed consolidated statement of financial condition and in Note 6 - Financial Assets and Financial Liabilities, are comprised of securities that the Company does not carry in its market making business, and include listed common stocks, corporate and municipal debt and mortgage backed and other asset backed securities. These investments are generally reported as Level 2 financial instruments, except for unrestricted listed equities, which are classified as Level 1 financial instruments. The fair values of other fair value investments are determined using broker and vendor prices that have been independently validated by the Company. Validation methods applied by the Company include comparisons of the broker and vendor prices to other independent pricing services and reviews of the underlying assumptions and other inputs (such as estimated cash flows, underlying default rates and variable interest rate sensitivity analysis) used by brokers or vendors to calculate these investments’ fair values.

	Earnings Per Share

	Earnings per share (“EPS”) are computed in accordance with ASC 260, Earnings per Share. Shares of Class A and Class B common stock share proportionately in the earnings of IBG, Inc. 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. 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 dilutive potential common shares.

	For periods prior to June 6, 2012 (Note 4), the Company has determined to reflect Topic D-98 measurement adjustments for non-fair value redemption rights through application of the two-class method of calculating earnings per share in lieu of recognizing the impact through the determination of net income attributable to common shareholders. Furthermore, in accordance with footnote 17 of ASC 480-10-S99-3A, the Company has elected to treat only the portion of the periodic measurement adjustments that reflect a redemption in excess of fair value as being akin to a dividend, reducing net income attributable to common stockholders for purposes of applying the two-class method. Decreases in the carrying amount of redeemable noncontrolling interests through Topic D-98 measurement adjustments are reflected in the application of the two-class method only to the extent they represent recoveries of amounts previously accounted for by applying the two-class method.

	Stock-Based Compensation

	IBG, Inc. follows ASC 718, Compensation—Stock Compensation, to account for its stock-based compensation plans. ASC 718 requires all share-based payments to employees to be recognized in the financial statements using a fair value-based method. As a result, IBG, Inc. expenses the fair value of awards granted to employees, generally 50% in the year of grant in recognition of plan forfeiture provisions (described below) and the remaining 50% over the related vesting period utilizing the “graded vesting” method permitted under ASC 718-10. In the case of “retirement eligible” employees (those employees older than 59), 100% of awards are expensed when granted.

	Awards granted under the 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

	IBG, Inc. defines cash equivalents as short-term, highly liquid securities and cash deposits, other than those used to support margin and clearing requirements or assets held in segregated accounts 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. In addition, substantially all of the Operating Companies are members of various clearing organizations at which cash or securities are deposited as required to conduct day-to-day clearance activities. Securities segregated for regulatory purposes consisted of U.S. Treasury Bills of $2.50 billion and $2.30 billion at September 30, 2013 and December 31, 2012, respectively, which are recorded as Level 1 financial assets and securities purchased under agreements to resell in the amount of $6.51 billion and $6.37 billion as of September 30, 2013 and December 31, 2012, respectively, which amounts approximate fair value.

	Securities Borrowed and Securities Loaned

	Securities borrowed and securities loaned are recorded at the amount of 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, IBG, Inc. 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.

	IBG, Inc. monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as permitted contractually. Receivables and payables with the same counterparty are not offset in the unaudited condensed consolidated statements of financial condition. For these transactions, the fees received or paid by IBG, Inc. are recorded as interest income or interest expense in the unaudited 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. The Company’s policy is to obtain possession of collateral with a fair value equal to or in excess of the principal amount loaned under resale agreements. To ensure that the fair value of the underlying collateral remains sufficient, this collateral is valued daily with additional collateral obtained or excess collateral returned, as permitted under contractual provisions. The Company does not net securities purchased under agreements to resell transactions with securities sold under agreements to repurchase transactions entered into with the same counterparty.

Financial Instruments Owned and Sold But Not Yet Purchased

Financial instrument transactions are accounted for on a trade date basis. Financial instruments owned and financial instruments sold but not yet purchased are recorded 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 classified as financial instruments owned and pledged as collateral in the unaudited condensed consolidated statements of financial condition.

IBG, Inc. 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 reported as components of financial instruments owned or financial instruments sold but not yet purchased in the unaudited 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 unaudited condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are expensed as a component of general and administrative expense.

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 IBG, Inc. 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 IBG, Inc. from a seller by the settlement date (“fails to receive”).

Investments

IBG, Inc. makes certain strategic investments related to financial services and accounts for these investments under the cost method of accounting or under the equity method of accounting as required under ASC 323, Investments—Equity Method and Joint Ventures. Investments are accounted for under the equity method of accounting when IBG, Inc. has significant influence over the investee. 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 IBG, Inc.’s initial investment and adjusted each period for IBG, Inc.’s share of the investee’s income or loss. IBG, Inc.’s share of the income or losses from equity investments is reported as a component of other income in the unaudited condensed consolidated statements of comprehensive income. The recorded amounts of IBG, Inc.’s equity method investments, $27.0 million at September 30, 2013 ($34.7 million at December 31, 2012), which are reported as a component of other assets in the unaudited condensed consolidated statements of financial condition, increase or decrease accordingly. Contributions paid to and distributions received from equity investees are recorded as additions or reductions, respectively, to the respective investment balance.

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. IBG, Inc.’s equity investments do not have readily determinable market values. All equity method investments are reviewed for changes in circumstances or occurrence of events that suggest IBG, Inc.’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. IBG, Inc. 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, $27.8 million at September 30, 2013 ($36.2 million at December 31, 2012), 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 components of other assets in the unaudited condensed consolidated statements of financial condition. Dividends received from cost basis investments are recognized as a component of other income as such dividends are received.

The Company also makes other fair value investments (which are not considered core business activities) that are accounted for at fair value (Note 6), with gains and losses recorded as a component of other income.

Property and Equipment

Property and equipment, which is a component of other assets, 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 unaudited condensed consolidated statement of comprehensive income pursuant to 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 statement of comprehensive income, but are excluded from reported net income. IBG, Inc.’s OCI is comprised of foreign currency translation adjustments, net of related income taxes, where applicable.

IBG, Inc.’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 are reported as a component of accumulated OCI. In general, the practice and intention of the Company is to reinvest the earnings of its non-U.S. subsidiaries in those operations. Deferred income taxes have not been provided for U.S. tax liabilities or for additional foreign taxes on unremitted earnings that have been indefinitely reinvested.

Revenue Recognition

—Trading Gains

Trading gains and losses are recorded on trade date and are reported on a net basis. Trading gains are comprised of changes in the fair value of financial instruments owned and financial instruments sold but not yet purchased (i.e., unrealized gains and losses) and realized gains and losses. 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 and financial instruments sold but not yet purchased are reported on a net basis as a component of trading gains in the accompanying unaudited 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 in the unaudited condensed consolidated statements of comprehensive income, and the related expenses are reported as execution and clearing expenses, also on a trade date basis.

—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. Such interest is recorded on the accrual basis.

—Foreign Currency Transaction Gains and Losses

Foreign currency transaction gains and losses from market making are reported as a component of trading gains in the unaudited condensed consolidated statements of comprehensive income. Electronic brokerage foreign currency transaction gains and losses are included in interest (if arising from currency swap transactions) or other income.

Income Taxes

IBG, Inc. accounts for income taxes in accordance with ASC 740, Income Taxes. The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits are based on enacted tax laws (Note 11) and reflect management’s best assessment of estimated future taxes to be paid. The Company is subject to income taxes in both the United States and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates.

Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statement 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. Management 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 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 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 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 2013, prior to the issuance of the Company’s unaudited condensed consolidated financial statements, ASUs 2013-01 through 2013-11 have been issued. Following is a summary of recently issued ASUs that have affected or may affect the Company’s unaudited condensed consolidated financial statements:

		Affects	Status

ASU 2011-11		Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities	Effective for fiscal periods beginning on or after January 1, 2013. Retrospective disclosures have been made for comparative periods presented.

ASU 2013-01		Balance Sheet (Topic 210): Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities	Effective for fiscal periods beginning on or after January 1, 2013 (the same as the effective date of ASU 2011-11).

ASU 2013-02		Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income	Effective for fiscal periods beginning on or after December 15, 2012.

ASU 2013-04		Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation Is Fixed at the Reporting Date	Effective prospectively for fiscal periods beginning on or after December 15, 2013. Early adoption is permitted.

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. Early adoption is permitted.

Adoption of those ASUs that became effective during 2013, prior to the issuance of the Company’s unaudited condensed consolidated financial statements, did not have a material effect on those financial statements. Management is assessing the potential impact on the Company’s financial statements of adopting ASUs that will become effective in the future.

Trading_Activities_and_Related

Trading Activities and Related Risks	3 Months Ended
	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Trading Activities and Related Risks	'
	3. Trading Activities and Related Risks

	IBG, Inc.’s trading activities include providing securities market making and brokerage services. Trading activities expose IBG, Inc. 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 IBG, Inc.’s risk-taking is consistent with its business strategy, capital structure, and current and anticipated market conditions.

	Market Risk

	IBG, Inc. 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. IBG, Inc. 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. IBG, Inc. 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. IBG, Inc. is subject to equity price risk primarily in financial instruments owned and sold but not yet purchased. IBG, Inc. 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. Exchange rate contracts may include cross-currency swaps and currency futures contracts. Currency swaps are agreements to exchange future payments in one currency for payments in another currency. These agreements are used to effectively convert assets or liabilities denominated in different currencies. Currency futures are contracts for delayed delivery of currency at a specified future date. IBG, Inc. uses currency swaps to manage the levels of its non-U.S. dollar currency balances and currency cash and futures to hedge its global exposure.

	Interest Rate Risk

	Interest rate risk arises from the possibility that changes in interest rates will affect the value of financial instruments. IBG, Inc. is exposed to interest rate risk on cash and margin balances, positions carried in equity securities, options, futures and on its debt obligations. These risks are managed through investment policies and by entering into interest rate futures contracts.

	Credit Risk

	IBG, Inc. 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 IBG, Inc. to default risk. IBG, Inc. 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. IBG, Inc. 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 IBG, Inc. that exposes IBG, Inc. to default risk arising from the potential that customers or counterparties may fail to satisfy their obligations. In these situations, IBG, Inc. 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, IBG, Inc. may purchase the underlying security in the market and seek reimbursement for any losses from the counterparty.

	For cash management purposes, IBG, Inc. 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. In accordance with industry practice, repos are collateralized by securities with a market value in excess of the obligation under the contract. Similarly, securities borrowed and loaned agreements are collateralized by deposits of cash or securities. IBG, Inc. 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 IBG, Inc. as permitted under contractual provisions.

	Concentrations of Credit Risk

	IBG, Inc.’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, 2013, the Company did not have any material concentrations of credit risk outside the ordinary course of business.

	Off-Balance Sheet Risks

	IBG, Inc. may be exposed to a risk of loss not reflected in the unaudited 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 IBG, Inc.’s cost to liquidate such contracts may exceed the amounts reported in IBG, Inc.’s unaudited condensed consolidated statements of financial condition.

Equity_and_Earnings_Per_Share

Equity and Earnings Per Share	3 Months Ended
Equity and Earnings Per Share	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Equity and Earnings Per Share	'
	4. Equity and Earnings Per Share

	In connection with its initial public offering of Class A common stock (“IPO”) in May 2007, IBG, Inc. purchased 10.0% of the membership interests in IBG LLC from Holdings, became the sole managing member of IBG LLC and began to consolidate IBG LLC’s financial results into its financial statements. Holdings wholly owns all Class B common stock, which common stock has voting rights in proportion to its ownership interests in IBG LLC, approximately 87.6% as of September 30, 2013. The consolidated financial statements reflect the results of operations and financial position of IBG, Inc., including consolidation of its investment in IBG LLC. Prior to the June 6, 2012 amendment to the Exchange Agreement (described below), Holdings’ ownership interests in IBG LLC were accounted for and reported in these consolidated financial statements as “redeemable noncontrolling interests” (temporary equity) pursuant to ASC 810-10-45, ASC 815-40-25 and ASC 480-10-S99-3A. For periods after the Amendment, beginning with the quarter ended June 30, 2012, the noncontrolling interests in IBG LLC attributable to Holdings are reported as a component of total equity, 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, 2013 and December 31, 2012, 1,000,000,000 shares of Class A common stock were authorized, of which 50,096,562 and 47,797,844 shares have been issued; and 49,971,727 and 47,499,739 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, 2013 and December 31, 2012, respectively. In addition, 10,000 shares of preferred stock have been authorized, of which no shares are issued or outstanding as of September 30, 2013 and December 31, 2012, respectively.

	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 redemption of Holdings member interests in exchange for common stock, which deferred tax assets are a component of other assets in the unaudited condensed consolidated statement of financial condition and are being amortized as additional deferred income tax expense over 15 years from the IPO date and from the 2011 redemption date, respectively, as allowable under current tax law. As of September 30, 2013 and December 31, 2012, the unamortized balance of these deferred tax assets was $266.6 million and $281.6 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 unaudited condensed consolidated statement of financial condition.

	The remaining 15% is accounted for as a permanent increase to additional paid-in capital in the unaudited condensed consolidated statement 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, 2013 were $387.1 million, $329.0 million and $58.1 million, respectively. Amounts payable under the Tax Receivable Agreement are payable to Holdings annually upon the filing of IBG, Inc.’s federal income tax return. The Company has paid Holdings a total of $70.4 million through September 30, 2013 pursuant to the terms of the Tax Receivable Agreement.

	The Exchange Agreement 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 Company’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, the Company issued 1,983,624 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 (Note 10), IBG, Inc.’s interest in IBG LLC has increased to approximately 12.4%, with Holdings owning the remaining 87.6% as of September 30, 2013. 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 86.4% at September 30, 2013.

	The Exchange Agreement, as amended June 6, 2012, provides that the Company may facilitate the redemption by Holdings of interests held by its members through the issuance of shares of common stock through a public offering in exchange for the interests in IBG LLC being redeemed by Holdings. The Amendment eliminated from the Exchange Agreement an alternative funding method, which provided that upon approval by the board of directors and by agreement of the Company, IBG LLC and Holdings, redemptions could be made in cash.

	Subsequent to the amendment to the Exchange Agreement on June 6, 2012, the Company recorded adjustments to report Holdings’ noncontrolling interests in IBG LLC as component of total equity, reducing redeemable noncontrolling interests to zero and reversing the cumulative effect of adjustments through June 6, 2012 to redemption value previously recorded to additional paid-in capital. The effect of these adjustments was:

	(in thousands)	Adjustments
		as of June 6,
		2012
	Redeemable noncontrolling interests	$(5,367,553	)
	Additional Paid in Capital	$472,409
	Retained earnings	$572,840
	Noncontrolling interests	$4,322,304

	Earnings per Share

	For periods prior to June 6, 2012, the Company reflected measurement adjustments for non-fair value redemption rights through application of the two-class method of calculating earnings per share in lieu of recognizing the impact through the determination of net income attributable to common stockholders.


	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:

			Three months ended						Nine months ended
			September 30,						September 30,
			2013			2012			2013			2012
	Basic earnings per share:
	Net income attributable to common stockholders	$	16,447		$	12,488		$	33,382		$	31,556
	Add (deduct) net income attributable to non-fair value redemption rights		-			-			-			1,108
	Net income available for common stockholders	$	16,447		$	12,488		$	33,382		$	32,664

	Weighted average shares of common stock outstanding:
	Class A		49,965,950			47,488,359			48,807,221			46,588,113
	Class B		100			100			100			100
			49,966,050			47,488,459			48,807,321			46,588,213

	Basic earnings per share	$	0.33		$	0.26		$	0.68		$	0.70


	Diluted earnings (loss) 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:

		Three months ended						Nine months ended
		September 30,						September 30,
		2013			2012			2013			2012
Diluted earnings per share:
Net income available for common stockholders	$	16,447		$	12,488		$	33,382		$	32,664

Weighted average shares of common stock outstanding:
Class A:
Issued and outstanding		49,965,950			47,488,359			48,807,221			46,588,113
Potentially dilutive common shares issuable pursuant to employee incentive plans		1,022,164			191,359			1,174,343			277,557
Class B		100			100			100			100
		50,988,214			47,679,818			49,981,664			46,865,770

Diluted earnings per share	$	0.32		$	0.26		$	0.67		$	0.70

Member and Stockholder Dividends

Through September 30, 2013, IBG LLC paid dividends totaling $122.7 million to its members, of which IBG, Inc.’s proportionate share was $15.0 million. In March, June and September 2013, the Company paid cash dividends of $0.10 per share of Common Stock, totaling $4.7 million, $5.0 million and $5.0 million, respectively.

On October 15, 2013, the Company declared a cash dividend of $0.10 per common share, payable on December 13, 2013 to shareholders of record as of November 29, 2013.

Comprehensive_Income

Comprehensive Income	3 Months Ended
Comprehensive Income	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Comprehensive Income [Text Block]	'
	5. Comprehensive Income

	Comprehensive income is comprised of Net Income and Other Comprehensive Income (“OCI”). The Company’s OCI is comprised of foreign currency translation adjustments, which arise from changes in the U.S. dollar value of the net worth of the Company’s subsidiaries whose functional currency is other than U.S. dollars during respective reporting periods. The following table presents comprehensive income and earnings per share on comprehensive income (calculated using the two-class method for periods prior to June 6, 2012):

			Three months ended				Nine months ended
			September 30,				September 30,
			2013		2012		2013		2012

	Comprehensive income attributable to common stockholders, net of tax	$	20,077	$	14,382	$	29,666	$	32,370
	Add (deduct) net income attributable to non-fair value redemption rights		-		-		-		1,108

	Comprehensive income available for common stockholders	$	20,077	$	14,382	$	29,666	$	33,478


	Earnings per share on comprehensive income:
	Basic	$	0.40	$	0.30	$	0.61	$	0.72
	Diluted	$	0.39	$	0.30	$	0.59	$	0.71


	Weighted average common shares outstanding:
	Basic		49,966,050		47,488,459		48,807,321		46,588,213
	Diluted		50,988,214		47,679,818		49,981,664		46,865,770

Fair_Value

Fair Value	3 Months Ended
Fair Value	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Fair value	'
	6. Financial Assets and Financial Liabilities

	Fair Value

	The following tables set forth, by level within the fair value hierarchy (Note 2), financial assets and liabilities, primarily financial instruments owned and financial instruments sold, but not yet purchased at fair value as of September 30, 2013 and December 31, 2012. As required by ASC 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, 2013

			Level 1			Level 2			Level 3			Total

	Securities segregated for regulatory purposes	$	2,500,627		$	-		$	-		$	2,500,627
	Financial instruments owned:
	Stocks		1,167,306			-			181			1,167,487
	Options		2,119,958			19,426			-			2,139,384
	Warrants and discount certificates		55,392			-			-			55,392
	U.S. and foreign government obligations		1,967			2,309			-			4,276
	Corporate and municipal bonds		64,057			20,148			-			84,205
	Currency forward contracts		-			4,153			-			4,153
	Total financial instruments owned		3,408,680			46,036			181			3,454,897

	Financial instruments owned and pledged as collateral:
	Stocks		865,051			-			-			865,051
	Warrants		312			-			-			312
	U.S. and foreign government obligations		103,015			-			-			103,015
	Corporate and municipal bonds		1,998			-			-			1,998
	Total financial instruments owned and pledged as collateral		970,376			-			-			970,376

	Subtotal		4,379,056			46,036			181			4,425,273

	Other fair value investments, included in other assets:
	Stocks		7,545			407			-			7,952
	Corporate and municipal bonds		1,820			39,120			-			40,940
	Mortgage backed securities		-			28,081			-			28,081
	Other asset backed securities		-			14,607			-			14,607
	Other		-			8,717			-			8,717

	Total Financial Assets at Fair Value	$	6,889,048		$	136,968		$	181		$	7,026,197

			Financial Liabilities At Fair Value as of September 30, 2013

			Level 1			Level 2			Level 3			Total
	Financial instruments sold, not yet purchased:
	Stocks	$	1,443,990		$	-		$	64		$	1,444,054
	Options		2,058,289			9,084			-			2,067,373
	Warrants and discount certificates		1,640			-			-			1,640
	U.S. and foreign government obligations		-			1,229			-			1,229
	Corporate bonds		70,056			7,981			-			78,037
	Currency forward contracts		-			959			-			959
	Total financial instruments sold, not yet purchased	$	3,573,975		$	19,253		$	64		$	3,593,292


			Financial Assets At Fair Value as of December 31, 2012

			Level 1			Level 2			Level 3			Total

	Securities segregated for regulatory purposes	$	2,297,024		$	-		$	-		$	2,297,024
	Financial instruments owned:
	Stocks		887,031			-			-			887,031
	Options		2,388,173			-			-			2,388,173
	Warrants and discount certificates		147,317			-			-			147,317
	U.S. and foreign government obligations		30,087			-			-			30,087
	Corporate and municipal bonds		104,387			59,533			-			163,920
	Currency forward contracts		-			1,351			-			1,351
Total financial instruments owned		3,556,995			60,884			-			3,617,879

Financial instruments owned and pledged as collateral:
Stocks		775,222			-			-			775,222
Warrants		350			-			-			350
U.S. and foreign government obligations		146,953			-			-			146,953
Corporate and municipal bonds		4,332			-			-			4,332
Total financial instruments owned and pledged as collateral		926,857			-			-			926,857

Subtotal		4,483,852			60,884			-			4,544,736

Other fair value investments, included in other assets:
Stocks		17,707			3,549			-			21,256
Corporate and municipal bonds		2,249			53,325			-			55,574
Mortgage backed securities		-			21,311			-			21,311
Other asset backed securities		-			17,023			-			17,023
Other		-			1,068			-			1,068

Total Financial Assets at Fair Value	$	6,800,832		$	157,160		$	-		$	6,957,992

		Financial Liabilities At Fair Value as of December 31, 2012

		Level 1			Level 2			Level 3			Total
Financial instruments sold, not yet purchased:
Stocks	$	1,787,741		$	-		$	-		$	1,787,741
Options		2,389,871			-			-			2,389,871
Warrants and discount certificates		2,104			-			-			2,104
U.S. and foreign government obligations		451			-			-			451
Corporate bonds		90,710			11,833			-			102,543
Currency forward contracts		-			3,550			-			3,550
Total financial instruments sold, not yet purchased	$	4,270,877		$	15,383		$	-		$	4,286,260

Transfers Between Level 1 and Level 2

Transfers of financial instruments owned and sold, not yet purchased 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 three months ended September 30, 2013 the Company reclassified $0.2 million of financial instruments owned from Level 1 to Level 2 and reclassified approximately $0.2 million from Level 2 to Level 1. Financial instruments sold, but not yet purchased of approximately $0.5 million were reclassified from Level 1 to Level 2 and approximately $0.6 million were reclassified from Level 2 to Level 1.

During the nine months ended September 30, 2013, the Company reclassified approximately $1.7 million of financial instruments owned 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 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.

There were no transfers of financial instruments to or from Level 1 and Level 2 during the three and nine months ended September 31, 2012.

Level 3 Financial Assets and Financial Liabilities

The Company’s Level 3 financial assets and financial liabilities are comprised of financial instruments owned. The following tables report Level 3 activities for the three and nine months ended September 30, 2013:

Financial assets – Level 3 activities:

		Delisted
		Securities
Balance, January 1, 2013	$	-
Total gains or losses (realized/unrealized)
- Included in earnings		(184)
Purchases, issuances and settlements		-
Transfers in and/or out of Level 3		365

Balance, September 30, 2013	$	181
Financial liabilities – Level 3 activities:
		Delisted
		Securities
Balance, January 1, 2013	$	-
Total gains or losses (realized/unrealized)
- Included in earnings		77
Purchases, issuances and settlements		-
Transfers in and/or out of Level 3		(13)

Balance, September 30, 2013	$	64

There were no Level 3 activities, including transfers, for the three and nine months ended September 30, 2012.


Netting of Financial Assets and Financial Liabilities

The Company adopted the guidance in ASU 2013-01, Balance Sheet (Topic 210): Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities for periods beginning after January 1, 2013. This authoritative guidance requires companies to report disclosures of offsetting assets and liabilities. The Company has applied the guidance retrospectively to the year ended 2012 and has included, in tabular format, the gross and net amounts of certain financial instruments in quarterly filings to date.

The Company does not net securities segregated for regulatory purposes, and securities borrowed and securities loaned are presented on a gross basis in the unaudited condensed consolidated statements of financial condition. In the tables below, the amounts of derivative financial instruments owned that are not offset in the unaudited 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 derivitive financial instruments.

The following table sets forth the netting of financial assets and of financial liabilities as of September 30, 2013 and December 31, 2012, pursuant to the requirements of ASU 2011-11 and ASU 2013-01 (millions).

		30-Sep-13
											Gross Amounts Not Offset in the
											Condensed Consolidated Statement of
											Financial Condition
				Gross Amounts			Net Amounts of
				Offset in the			Assets Presented in
				Condensed			the Condensed
	Gross Amounts of			Consolidated			Consolidated
	Recognized			Statement of			Statement of				Financial			Cash Collateral
	Assets			Financial Condition			Financial Condition				Instruments			Received		Net Amount
Offsetting of Financial Assets:
Securities segregated for regulatory purposes -
purchased under agreements to resell	$	6,510.1	(1)	$	-		$	6,510.1		$	(6,510.1	)	$	-	$	-
Securities borrowed		3,363.2			-			3,363.2			(3,363.2	)		-		-
Securities purchased under agreements to resell		487.8			-			487.8			(487.8	)		-		-
Financial Instruments owned:
Options		2,139.4			-			2,139.4			(1,945.1	)		-		194.3
Warrants and discount certificates		55.4			-			55.4			(1.6	)		-		53.8
Currency forward contracts		4.2			-			4.2			-			-		4.2
Total	$	12,560.1		$	-		$	12,560.1		$	(12,307.8	)	$	-	$	252.3





											Gross Amounts Not Offset in the
											Condensed Consolidated Statement of
											Financial Condition
				Gross Amounts			Net Amounts of
				Offset in the			Liabilities Presented
				Condensed			in the Condensed
	Gross Amounts of			Consolidated			Consolidated
	Recognized			Statement of			Statement of				Financial			Cash Collateral
	Liabilities			Financial Condition			Financial Condition				Instruments			Pledged		Net Amount
Offsetting of Financial Liabilities:
Securities loaned	$	2,193.0		$	-		$	2,193.0		$	(2,193.0	)	$	-	$	-
Financial instruments sold, not yet purchased:
Options		2,067.4			-			2,067.4			(1,945.1	)		-		122.3
Warrants and discount certificates		1.6			-			1.6			(1.6	)		-		-
Currency forward contracts		1.0			-			1.0			-			-		1.0
Total	$	4,263.0		$	-		$	4,263.0		$	(4,139.7	)	$	-	$	123.3


		31-Dec-12
											Gross Amounts Not Offset in the
											Condensed Consolidated Statement of
											Financial Condition
				Gross Amounts			Net Amounts of
				Offset in the			Assets Presented in
				Condensed			the Condensed
	Gross Amounts of			Consolidated			Consolidated
	Recognized			Statement of			Statement of				Financial			Cash Collateral
	Assets			Financial Condition			Financial Condition				Instruments			Received		Net Amount
Offsetting of Financial Assets:
Securities segregated for regulatory purposes -
purchased under agreements to resell	$	6,366.4	(1)	$	-		$	6,366.4		$	(6,366.4	)	$	-	$	-
Securities borrowed		2,833.1			-			2,833.1			(2,833.1	)		-		-
Securities purchased under agreements to resell		428.9			-			428.9			(428.9	)		-		-
Financial Instruments owned:
Options		2,388.2			-			2,388.2			(2,202.1	)		-		186.1
Warrants and discount certificates		147.3			-			147.3			(2.1	)		-		145.2
Currency forward contracts		1.4			-			1.4			-			-		1.4
Total	$	12,165.3		$	-		$	12,165.3		$	(11,832.6	)	$	-	$	332.7





											Gross Amounts Not Offset in the
											Condensed Consolidated Statement of
											Financial Condition
				Gross Amounts			Net Amounts of
				Offset in the			Liabilities Presented
				Condensed			in the Condensed
	Gross Amounts of			Consolidated			Consolidated
	Recognized			Statement of			Statement of				Financial			Cash Collateral
	Liabilities			Financial Condition			Financial Condition				Instruments			Pledged		Net Amount
Offsetting of Financial Liabilities:
Securities loaned	$	1,839.3		$	-		$	1,839.3		$	(1,839.3	)	$	-	$	-
Financial instruments sold, not yet purchased:
Options		2,389.9			-			2,389.9			(2,202.1	)		-		187.8
Warrants and discount certificates		2.1			-			2.1			(2.1	)		-		-
Currency forward contracts		3.6			-			3.6			-			-		3.6
Total	$	4,234.9		$	-		$	4,234.9		$	(4,043.5	)	$	-	$	191.4

	-1	As of September 30, 2013 and December 31, 2012, the company had $6.51 billion and $6.37 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 unaudited condensed consolidated statements of financial condition.

Collateralized_Transactions

Collateralized Transactions	3 Months Ended
Collateralized Transactions	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
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 repurchase agreements, 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 Company 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 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 account and an overall evaluation of the 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, 2013 and December 31, 2012, approximately $12.73 billion and $9.85 billion, respectively, of customer margin loans were outstanding.

	Amounts relating to collateralized transactions at September 30, 2013 and December 31, 2012 are summarized as follows (millions):

			September 30, 2013				December 31, 2012 (2)

				Permitted		Sold or		Permitted		Sold or
				to Repledge		Repledged		to Repledge		Repledged

	Securities lending transactions		$	9,082.1	$	2,941.5	$	5,323.7	$	2,699.2
	Agreements to resell (1)			7,003.6		7,003.6		6,778.8		6,778.8
	Customer margin securities			10,304.0		3,609.2		13,603.7		3,016.3
			$	26,389.7	$	13,554.3	$	25,706.2	$	12,494.3


		-1	At September 30, 2013, $6.51 billion or 93% (at December 31, 2012, $6.37 billion, or 94%), 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.

		-2	The Company has revised its reporting of collateral permitted to be repledged and collateral sold or repledged, primarily with respect to securities available for repledging under securities lending transactions in connection with the Company's Stock Yield Enhancement Program. Disclosures for December 31, 2012 have been conformed to the new presentation for comparability purposes.



	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, 2013 and December 31, 2012, the majority of the Company’s government obligations owned were pledged to clearing organizations.

	Financial instruments owned and pledged, including amounts pledged to affiliates, where the counterparty has the right to repledge, at September 30, 2013 and December 31, 2012 consisted of the following (millions):

				September 30,		December 31,
				2013		2012
	Stocks		$	865.1	$	775.2
	Warrants			0.3		0.4
	U.S. and foreign government obligations			103.0		147.0
	Corporate and municipal bonds			2.0		4.3
			$	970.4	$	926.9

Senior_Notes_Payable

Senior Notes Payable	3 Months Ended
Senior Notes Payable	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Senior Notes Payable	'
	8. Senior Notes Payable

	In January 2012, the Company discontinued its Senior Notes Program. All previously issued Senior Notes, $101,411 outstanding as of December 31, 2011, were redeemed prior to June 30, 2012.

Senior_Secured_Revolving_Credi

Senior Secured Revolving Credit Facility	3 Months Ended
	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Senior Secured Revolving Credit Facility	'
	9. 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.

	IBG LLC is the sole borrower under this credit facility. The facility’s interest rate is indexed to the overnight federal funds rate or to the British Bankers Association LIBOR rate for the relevant term, at the borrower’s option, and is secured by a first priority interest in all of the capital stock of each entity owned directly by IBG LLC (subject to customary limitations with respect to foreign subsidiaries). The facility may be used to finance working capital needs and general corporate purposes, including downstreaming funds to IBG LLC’s regulated broker-dealer subsidiaries as regulatory capital. This allows IBG LLC to take advantage of market opportunities when they arise, while maintaining substantial excess regulatory capital. The financial condition covenants contained in this credit facility include the following:

		•	minimum consolidated shareholders’ equity, as defined, of $3.6 billion, with quarterly increases equal to 25% of positive consolidated net income;

		•	maximum total debt to capitalization ratio of 30%;

		•	minimum liquidity ratio of 1.0 to 1.0; and

		•	maximum total debt to net regulatory capital ratio of 35%.

	At September 30, 2013 and December 31, 2012, no borrowings were outstanding under this credit facility and IBG LLC was in compliance with all of the covenants. At maturity, subject to meeting certain terms of the facility, the Company will have an option to convert the facility to a one-year term loan.

Defined_Contribution_and_Emplo

Defined Contribution and Employee Incentive Plans	3 Months Ended
Defined Contribution and Employee Incentive Plans	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Employee Incentive Plans	'
	10. 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 will vest upon 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 shall vest on the fifth anniversary date of their grant and 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, 2013 and December 31, 2012, payables to employees for ROI Dollar Units were $5.5 million and $7.6 million, respectively, all of which were vested. These amounts are included in accounts payable, accrued expenses and other liabilities in the unaudited condensed consolidated statements of financial condition. Compensation expense for the ROI Dollar Unit plan, included in the unaudited condensed consolidated statements of comprehensive income was $0.5 million and $0.6 million for the nine months ended September 30, 2013 and September 30, 2012, respectively.

	2007 ROI Unit Stock Plan

	In connection with the IPO, IBG, Inc. adopted the Interactive Brokers Group, Inc. 2007 ROI Unit Stock Plan (the “ROI Unit Stock Plan”). Under this plan, certain employees of the Group 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 IBG, Inc. 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. Compensation expense for the 2007 ROI Unit Stock Plan and related grants under the 2007 Stock Incentive Plan, net of the effect of forfeitures, included in the unaudited condensed consolidated statements of comprehensive income for the nine months ended September 30, 2012 was $2.7 million. As of December 31, 2012, compensation costs for the ROI Unit Stock Plan had been fully accrued.

	2007 Stock Incentive Plan

	Under the Interactive Brokers Group, Inc. 2007 Stock Incentive Plan (the “Stock Incentive Plan” or “SIP”), up to 20.0 million shares of common stock may be granted and issued to directors, officers, employees, contractors and consultants of
	IBG, Inc. and its subsidiaries. The purpose of the Stock Incentive Plan is to promote IBG, Inc.’s long-term financial success by attracting, retaining and rewarding eligible participants.

	The Stock Incentive Plan is administered by the Compensation Committee of IBG, Inc.’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 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 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.

	IBG, Inc. 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 IBG, Inc. 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. 20,423 awards have been granted to the external directors cumulatively since the IPO.

	Stock Incentive Plan share grants (excluding 21,009 shares issued pursuant to the 2007 ROI Unit Stock Plan above) and the related fair values at the date of grant were:


						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
			17,284,454		$	302.4

	Estimated future grants under the Stock Incentive Plan are accrued for ratably during each year under the ASC 718 “Graded Vesting” method. Compensation expense recognized in the unaudited condensed consolidated statements of comprehensive income for the nine months ended September 30, 2013 and 2012 were $28.1 million and $51.2 million, respectively. Estimated future compensation costs for unvested awards at September 30, 2013 are $30.2 million.

	The following is a summary of Stock Plan activity for the period from January 1, 2013 through September 30, 2013:
			Shares
			2007 Stock		2007 ROI Unit
			Incentive Plan		Stock Plan

	Balance, December 31, 2012		12,402,482		169,289

	Granted		-		-
Forfeited		(308,925)		(6,423)
Distributed (1)		(2,309,122)		(162,866)
Balance, September 30, 2013		9,784,435		-

(1) Shares distributed under the 2007 Stock Incentive Plan include 10,404 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.

Awards granted under the ROI Unit Stock Plan and the Stock Incentive Plan 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. 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, 2013, a total of 78,312 shares have been distributed under these post-employment provisions. These distributions are included in the Stock Plans activity tables above.

Income_Taxes

Income Taxes	3 Months Ended
Income Taxes	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Income taxes	'
	11. Income Taxes

	Income tax expense for the three and nine months ended September 30, 2013 and 2012 differs from the U.S. federal statutory rate due to 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 (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 tax return purposes.

	At September 30, 2013, accumulated earnings held by non-U.S. subsidiaries totaled $1.06 billion (at December 31, 2012 $969.8 million). Of this amount, approximately $416.7 million (at December 31, 2012 $380.6 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 $315.5 million and $297.5 million as of September 30, 2013 and December 31, 2012, 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 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	3 Months Ended
Commitments, Contingencies and Guarantees	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Commitments, Contingencies and Guarantees	'
	12. Commitments, Contingencies and Guarantees

	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. IBG, Inc. 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.

	On February 3, 2010, Trading Technologies International, Inc. (“Trading Technologies”) filed a complaint in the United States District Court for the Northern District of Illinois, Eastern Division, against Interactive Brokers Group, Inc., IBG LLC, Holdings, and Interactive Brokers LLC. Thereafter, Trading Technologies dismissed Interactive Brokers Group, Inc. and Holdings from the case, leaving only IBG LLC and Interactive Brokers LLC as defendants (“Defendants”). The operative complaint, as amended, alleges that the Defendants have infringed and continue to infringe twelve U.S. patents held by Trading Technologies. Trading Technologies is seeking, among other things, unspecified damages and injunctive relief. The case is in the early stages and discovery has yet to begin. While it is too early to predict the outcome of the matter, we believe we have meritorious defenses to the allegations made in the complaint and intend to defend ourselves vigorously against them. However, litigation is inherently uncertain and there can be no guarantee that the Company will prevail or that the litigation can be settled on favorable terms.

	IBG, Inc. accounts for potential losses related to litigation in accordance with ASC 450, Contingencies. As of September 30, 2013 and December 31, 2012, 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 ASC 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 unaudited 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 unaudited 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	3 Months Ended
Segment and Geographic Information	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Segment and Geographic Information	'
	13. Segment and Geographic Information

	IBG, Inc. operates in two business segments: electronic brokerage and market making. 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. IBG, Inc. conducts its electronic brokerage business through its Interactive Brokers subsidiaries, which provide electronic execution and clearing services to customers worldwide.

	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, 2013 and 2012, and to total assets as of September 30, 2013 and December 31, 2012 (millions):

			Three months ended							Nine months ended
			September 30,							September 30,
			2013			2012				2013		2012
	Net revenues:
	Electronic brokerage	$	194.7		$	167.6			$	602.5	$	498.3
	Market making		130.9			154.1				221.9		387.8
	Corporate and eliminations		0.7			(3.1	)			1.9		(2.7	)
	Total net revenues	$	326.3		$	318.6			$	826.3	$	883.4

	Income before income taxes:
	Electronic brokerage	$	108.4		$	80.8			$	342.7	$	254.4
	Market making		87.5			90.2				66.1		180.2
	Corporate and eliminations		0.5			1.6				3.7		(3.8	)
	Total income before income taxes	$	196.4		$	172.6			$	412.5	$	430.8


			September 30,				December 31,
			2013				2012
	Assets:
	Electronic brokerage	$	29,612.5			$	25,741.5
	Market making		12,513.3				12,730.8
	Corporate and eliminations		(5,848.8	)			(5,272.7	)
	Total assets	$	36,277.0			$	33,199.6

	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 IBG, Inc.’s net revenues are generated by subsidiaries operating outside the United States. International operations are comprised of electronic brokerage and market making activities in 23 countries in Europe, Asia and the Americas (outside the United States). The following table presents total net revenues and income before income taxes by geographic area for the three and nine months ended September 30, 2013 and 2012 (millions):
			Three months ended							Nine months ended
			September 30,							September 30,
			2013			2012				2013		2012
	Net revenues:
	United States	$	265.4		$	237.1			$	597.3	$	645.4
	International		59.5			86.0				227.2		243.4
	Corporate and eliminations		1.4			(4.5	)			1.8		(5.4	)
	Total net revenues	$	326.3		$	318.6			$	826.3	$	883.4

	Income before income taxes:
	United States	$	180.9		$	134.1			$	331.9	$	348.0
	International		14.3			38.3				76.9		89.1
	Corporate and eliminations		1.2			0.2				3.7		(6.3	)
	Total income before income taxes	$	196.4		$	172.6			$	412.5	$	430.8

Regulatory_Requirements

Regulatory Requirements	3 Months Ended
Regulatory Requirements	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Regulatory Requirements	'
	14. Regulatory Requirements

	At September 30, 2013, aggregate excess regulatory capital for all of the Operating Companies was $2.91 billion.

	TH LLC and IB LLC are subject to the Uniform Net Capital Rule (Rule 15c3-1) under the Exchange Act and the CFTC’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, 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 (formerly known as the U.K. Financial Services Authority) Capital Requirements Directive (formerly the financial resources requirement), 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 (millions):

			Net Capital/
			Eligible Equity		Requirement		Excess
	IB LLC	$	1,922.0	$	283.0	$	1,639.0
	TH LLC		470.0		50.5		419.5
	THE		654.3		169.3		485.0
	Other regulated Operating Companies		404.7		34.0		370.7
		$	3,451.0	$	536.8	$	2,914.2

	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 IBG, Inc. are subject to other regulatory restrictions and requirements.

	At September 30, 2013, all of the regulated Operating Companies were in compliance with their respective regulatory capital requirements.

Related_Party_Transactions

Related Party Transactions	3 Months Ended
Related Party Transactions	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Related Party Transactions	'
	15. 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 (Note 4).

	Included in receivables from and payables to customers in the accompanying unaudited condensed consolidated statements of financial condition as of September 30, 2013 and December 31, 2012 were accounts receivable from directors, officers and their affiliates of $14.3 million and $1.1 million and payables of $268.8 million and $745.0 million, respectively.

Subsequent_Events

Subsequent Events	3 Months Ended
Subsequent Events	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Subsequent events	'
	16. Subsequent Events

	As required by ASC 855-10-50, the Company has evaluated subsequent events for adjustment to or disclosure in its unaudited condensed consolidated financial statements through the date the unaudited condensed consolidated financial statements were issued.

	Recently, a small number of the Company's brokerage customers took relatively large positions in four securities 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 to the extent of approximately $68 million in aggregate, as measured shortly after the event. 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.

	No other recordable or disclosable events, not otherwise reported in these financial statements or the notes thereto, occurred.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	3 Months Ended
	Sep. 30, 2013
Significant accounting policies	'
Basis of Presentation	'
	Basis of Presentation

	These unaudited condensed consolidated financial statements are presented in U.S. dollars and have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding financial reporting with respect to Form 10-Q and accounting standards generally accepted in the United States of America (“U.S. GAAP”) promulgated in the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC” or the “Codification”). These unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries and include all adjustments of a normal, recurring nature necessary to present fairly the financial condition as of September 30, 2013 and December 31, 2012, the results of operations and comprehensive income for the three and nine months ended September 30, 2013 and 2012 and cash flows for the nine months ended September 30, 2013 and 2012. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in IBG, Inc.’s 2012 Annual Report on Form 10-K filed with the SEC on March 8, 2013. The condensed consolidated financial statement information as of December 31, 2012 has been derived from the 2012 audited consolidated financial statements. The results of operations for interim periods are not necessarily indicative of results for the entire year.
Principles of Consolidation	'
	Principles of Consolidation, including Noncontrolling Interests

	The unaudited 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 Group’s operations. In accordance with ASC 810, Consolidation, the Company consolidates the Group’s consolidated financial statements and records the interests in the Group that IBG, Inc. does not own as noncontrolling interests. Prior to the June 6, 2012 amendment (the “Amendment”) to the Exchange Agreement (Note 4), the Company was required to report IBG Holdings LLC’s (“Holdings”) ownership as redeemable noncontrolling interests (i.e., temporary equity) pursuant to ASC 810-10-45, ASC 815-40-25 and ASC 480-10-S99-3A (formerly FASB Emerging Issues Task Force Topic D-98), outside of total equity. Redemption value of these redeemable noncontrolling interests was measured as the number of equivalent shares of member interests in IBG LLC owned by Holdings multiplied by the then current market price per share of the Company’s common stock. The excess of the redemption value over the book value of these interests, which did not affect net income attributable to common stockholders or cash flows, was required to be accounted for as a reduction of the Company’s stockholders’ equity.

	The Company elected to recognize changes in redemption value in each reporting period immediately as they occurred as if the end of each reporting period was also the redemption date for the entire redeemable noncontrolling interest under paragraph 15(b) of ASC 480-10-S99-3A, notwithstanding that the redeemable noncontrolling interests are redeemable over a period of time pursuant to a redemption schedule (Note 4).

	For periods after the above referenced amendment, the noncontrolling interests in IBG LLC attributable to Holdings are reported as a component of equity.

	The Company’s policy is to consolidate all entities of which it owns more than 50% unless it does not have control. All inter-company balances and transactions have been eliminated. IBG, Inc. would also consolidate any Variable Interest Entities (“VIEs”) pursuant to ASC 860, Transfers and Servicing and ASC 810 of which it is the primary beneficiary. IBG, Inc. currently is not the primary beneficiary of any such entities and therefore no VIEs are included in the unaudited condensed consolidated financial statements.
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 the unaudited condensed consolidated financial statements and accompanying notes. Estimates, by their nature, are based on judgment and available information. Therefore, actual results could differ materially from those estimates. Such estimates include the estimated fair values of IBG LLC and the Company in connection with accounting for redeemable noncontrolling interests, the estimated value of investments accounted for under the equity method of accounting, the estimated useful lives of property and equipment, including capitalized internally developed software, the allowance for doubtful accounts, compensation accruals, current and deferred income taxes and estimated contingency reserves
Fair Value	'
	Fair Value

	At September 30, 2013 and December 31, 2012, substantially all of IBG, Inc.’s assets and liabilities, including financial instruments, were carried at fair value based on published market prices and were marked to market, or were assets which are short-term in nature and were carried at amounts that approximate fair value.

	IBG, Inc. applies the fair value hierarchy of ASC 820, Fair Value Measurement, 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; and
	Level 3	Prices or valuations that require inputs that are both significant to fair value measurement and unobservable.

	Financial instruments owned and financial instruments sold, but not yet purchased are generally classified as Level 1 financial instruments. 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 U.S. government and sovereign obligations, active listed securities, options, futures, options on futures and corporate and municipal debt securities. IBG, Inc. 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 financial instruments as such instruments are not exchange-traded. Other securities that are not traded in active markets are also classified in Level 2. 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, excluding securities subject to corporate actions that have a determinable external price, which remain classified as Level 1 securities.

	Other fair value investments, reported in other assets in the accompanying unaudited condensed consolidated statement of financial condition and in Note 6 - Financial Assets and Financial Liabilities, are comprised of securities that the Company does not carry in its market making business, and include listed common stocks, corporate and municipal debt and mortgage backed and other asset backed securities. These investments are generally reported as Level 2 financial instruments, except for unrestricted listed equities, which are classified as Level 1 financial instruments. The fair values of other fair value investments are determined using broker and vendor prices that have been independently validated by the Company. Validation methods applied by the Company include comparisons of the broker and vendor prices to other independent pricing services and reviews of the underlying assumptions and other inputs (such as estimated cash flows, underlying default rates and variable interest rate sensitivity analysis) used by brokers or vendors to calculate these investments’ fair values.
Earnings Per Share	'
	Earnings Per Share

	Earnings per share (“EPS”) are computed in accordance with ASC 260, Earnings per Share. Shares of Class A and Class B common stock share proportionately in the earnings of IBG, Inc. 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. 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 dilutive potential common shares.

	For periods prior to June 6, 2012 (Note 4), the Company has determined to reflect Topic D-98 measurement adjustments for non-fair value redemption rights through application of the two-class method of calculating earnings per share in lieu of recognizing the impact through the determination of net income attributable to common shareholders. Furthermore, in accordance with footnote 17 of ASC 480-10-S99-3A, the Company has elected to treat only the portion of the periodic measurement adjustments that reflect a redemption in excess of fair value as being akin to a dividend, reducing net income attributable to common stockholders for purposes of applying the two-class method. Decreases in the carrying amount of redeemable noncontrolling interests through Topic D-98 measurement adjustments are reflected in the application of the two-class method only to the extent they represent recoveries of amounts previously accounted for by applying the two-class method.
Stock-Based Compensation	'
	Stock-Based Compensation

	IBG, Inc. follows ASC 718, Compensation—Stock Compensation, to account for its stock-based compensation plans. ASC 718 requires all share-based payments to employees to be recognized in the financial statements using a fair value-based method. As a result, IBG, Inc. expenses the fair value of awards granted to employees, generally 50% in the year of grant in recognition of plan forfeiture provisions (described below) and the remaining 50% over the related vesting period utilizing the “graded vesting” method permitted under ASC 718-10. In the case of “retirement eligible” employees (those employees older than 59), 100% of awards are expensed when granted.

	Awards granted under the 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

	IBG, Inc. defines cash equivalents as short-term, highly liquid securities and cash deposits, other than those used to support margin and clearing requirements or assets held in segregated accounts for regulatory purposes.
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. In addition, substantially all of the Operating Companies are members of various clearing organizations at which cash or securities are deposited as required to conduct day-to-day clearance activities. Securities segregated for regulatory purposes consisted of U.S. Treasury Bills of $2.50 billion and $2.30 billion at September 30, 2013 and December 31, 2012, respectively, which are recorded as Level 1 financial assets and securities purchased under agreements to resell in the amount of $6.51 billion and $6.37 billion as of September 30, 2013 and December 31, 2012, 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 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, IBG, Inc. 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.

	IBG, Inc. monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as permitted contractually. Receivables and payables with the same counterparty are not offset in the unaudited condensed consolidated statements of financial condition. For these transactions, the fees received or paid by IBG, Inc. are recorded as interest income or interest expense in the unaudited 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. The Company’s policy is to obtain possession of collateral with a fair value equal to or in excess of the principal amount loaned under resale agreements. To ensure that the fair value of the underlying collateral remains sufficient, this collateral is valued daily with additional collateral obtained or excess collateral returned, as permitted under contractual provisions. The Company does not net securities purchased under agreements to resell transactions with 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 Sold But Not Yet Purchased

	Financial instrument transactions are accounted for on a trade date basis. Financial instruments owned and financial instruments sold but not yet purchased are recorded 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 classified as financial instruments owned and pledged as collateral in the unaudited condensed consolidated statements of financial condition.

	IBG, Inc. 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 reported as components of financial instruments owned or financial instruments sold but not yet purchased in the unaudited 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 unaudited condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are expensed as a component of general and administrative expense.
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 IBG, Inc. 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 IBG, Inc. from a seller by the settlement date (“fails to receive”).

Investments Policy	'
	Investments

	IBG, Inc. makes certain strategic investments related to financial services and accounts for these investments under the cost method of accounting or under the equity method of accounting as required under ASC 323, Investments—Equity Method and Joint Ventures. Investments are accounted for under the equity method of accounting when IBG, Inc. has significant influence over the investee. 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 IBG, Inc.’s initial investment and adjusted each period for IBG, Inc.’s share of the investee’s income or loss. IBG, Inc.’s share of the income or losses from equity investments is reported as a component of other income in the unaudited condensed consolidated statements of comprehensive income. The recorded amounts of IBG, Inc.’s equity method investments, $27.0 million at September 30, 2013 ($34.7 million at December 31, 2012), which are reported as a component of other assets in the unaudited condensed consolidated statements of financial condition, increase or decrease accordingly. Contributions paid to and distributions received from equity investees are recorded as additions or reductions, respectively, to the respective investment balance.

	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. IBG, Inc.’s equity investments do not have readily determinable market values. All equity method investments are reviewed for changes in circumstances or occurrence of events that suggest IBG, Inc.’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. IBG, Inc. 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, $27.8 million at September 30, 2013 ($36.2 million at December 31, 2012), 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 components of other assets in the unaudited condensed consolidated statements of financial condition. Dividends received from cost basis investments are recognized as a component of other income as such dividends are received.

	The Company also makes other fair value investments (which are not considered core business activities) that are accounted for at fair value (Note 6), with gains and losses recorded as a component of other income.
Property and Equipment	'
	Property and Equipment

	Property and equipment, which is a component of other assets, 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 unaudited condensed consolidated statement of comprehensive income pursuant to 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 statement of comprehensive income, but are excluded from reported net income. IBG, Inc.’s OCI is comprised of foreign currency translation adjustments, net of related income taxes, where applicable.

	IBG, Inc.’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 are reported as a component of accumulated OCI. In general, the practice and intention of the Company is to reinvest the earnings of its non-U.S. subsidiaries in those operations. Deferred income taxes have not been provided for U.S. tax liabilities or for additional foreign taxes on unremitted earnings that have been indefinitely reinvested.
Revenue Recognition	'
	Revenue Recognition

	—Trading Gains

	Trading gains and losses are recorded on trade date and are reported on a net basis. Trading gains are comprised of changes in the fair value of financial instruments owned and financial instruments sold but not yet purchased (i.e., unrealized gains and losses) and realized gains and losses. 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 and financial instruments sold but not yet purchased are reported on a net basis as a component of trading gains in the accompanying unaudited 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 in the unaudited condensed consolidated statements of comprehensive income, and the related expenses are reported as execution and clearing expenses, also on a trade date basis.

	—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. Such interest is recorded on the accrual basis.

	—Foreign Currency Transaction Gains and Losses

	Foreign currency transaction gains and losses from market making are reported as a component of trading gains in the unaudited condensed consolidated statements of comprehensive income. Electronic brokerage foreign currency transaction gains and losses are included in interest (if arising from currency swap transactions) or other income.
Income Taxes	'
	Income Taxes

	IBG, Inc. accounts for income taxes in accordance with ASC 740, Income Taxes. The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits are based on enacted tax laws (Note 11) and reflect management’s best assessment of estimated future taxes to be paid. The Company is subject to income taxes in both the United States and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates.

	Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statement 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. Management 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 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 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 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 2013, prior to the issuance of the Company’s unaudited condensed consolidated financial statements, ASUs 2013-01 through 2013-11 have been issued. Following is a summary of recently issued ASUs that have affected or may affect the Company’s unaudited condensed consolidated financial statements:

			Affects	Status

	ASU 2011-11		Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities	Effective for fiscal periods beginning on or after January 1, 2013. Retrospective disclosures have been made for comparative periods presented.

	ASU 2013-01		Balance Sheet (Topic 210): Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities	Effective for fiscal periods beginning on or after January 1, 2013 (the same as the effective date of ASU 2011-11).

	ASU 2013-02		Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income	Effective for fiscal periods beginning on or after December 15, 2012.

	ASU 2013-04		Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation Is Fixed at the Reporting Date	Effective prospectively for fiscal periods beginning on or after December 15, 2013. Early adoption is permitted.

	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. Early adoption is permitted.

	Adoption of those ASUs that became effective during 2013, prior to the issuance of the Company’s unaudited condensed consolidated financial statements, did not have a material effect on those financial statements. Management is assessing the potential impact on the Company’s financial statements of adopting ASUs that will become effective in the future.

Equity_and_Earnings_Per_Share_

Equity and Earnings Per Share (Tables)	3 Months Ended
Equity and Earnings Per Share (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Redeemable Noncontrolling Interests Adjustments	'
	(in thousands)	Adjustments
		as of June 6,
		2012
	Redeemable noncontrolling interests	$(5,367,553	)
	Additional Paid in Capital	$472,409
	Retained earnings	$572,840
	Noncontrolling interests	$4,322,304
Earnings per Share Basic and Diluted	'
	Three months ended					Nine months ended
			September 30,					September 30,
			2013		2012			2013		2012
	Basic earnings per share:
	Net income attributable to common stockholders	$	16,447	$	12,488		$	33,382	$	31,556
	Add (deduct) net income attributable to non-fair value redemption rights		-		-			-		1,108
	Net income available for common stockholders	$	16,447	$	12,488		$	33,382	$	32,664

	Weighted average shares of common stock outstanding:
	Class A		49,965,950		47,488,359			48,807,221		46,588,113
	Class B		100		100			100		100
			49,966,050		47,488,459			48,807,321		46,588,213

	Basic earnings per share	$	0.33	$	0.26		$	0.68	$	0.70


			Three months ended					Nine months ended
			September 30,					September 30,
			2013		2012			2013		2012
	Diluted earnings per share:
	Net income available for common stockholders	$	16,447	$	12,488		$	33,382	$	32,664

	Weighted average shares of common stock outstanding:
	Class A:
	Issued and outstanding		49,965,950		47,488,359			48,807,221		46,588,113
	Potentially dilutive common shares issuable pursuant to employee incentive plans		1,022,164		191,359			1,174,343		277,557
	Class B		100		100			100		100
			50,988,214		47,679,818			49,981,664		46,865,770

	Diluted earnings per share	$	0.32	$	0.26		$	0.67	$	0.70

Comprehensive_Income_Tables

Comprehensive Income (Tables)	3 Months Ended
Comprehensive Income (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Comprehensive Income Table	'
			Three months ended				Nine months ended
			September 30,				September 30,
			2013		2012		2013		2012

	Comprehensive income attributable to common stockholders, net of tax	$	20,077	$	14,382	$	29,666	$	32,370
	Add (deduct) net income attributable to non-fair value redemption rights		-		-		-		1,108

	Comprehensive income available for common stockholders	$	20,077	$	14,382	$	29,666	$	33,478


	Earnings per share on comprehensive income:
	Basic	$	0.40	$	0.30	$	0.61	$	0.72
	Diluted	$	0.39	$	0.30	$	0.59	$	0.71


	Weighted average common shares outstanding:
	Basic		49,966,050		47,488,459		48,807,321		46,588,213
	Diluted		50,988,214		47,679,818		49,981,664		46,865,770

Fair_Value_Tables

Fair Value (Tables)	3 Months Ended
Fair Value (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Fair Value Table	'
			Financial Assets At Fair Value as of September 30, 2013

			Level 1			Level 2			Level 3			Total

	Securities segregated for regulatory purposes	$	2,500,627		$	-		$	-		$	2,500,627
	Financial instruments owned:
	Stocks		1,167,306			-			181			1,167,487
	Options		2,119,958			19,426			-			2,139,384
	Warrants and discount certificates		55,392			-			-			55,392
	U.S. and foreign government obligations		1,967			2,309			-			4,276
	Corporate and municipal bonds		64,057			20,148			-			84,205
	Currency forward contracts		-			4,153			-			4,153
	Total financial instruments owned		3,408,680			46,036			181			3,454,897

	Financial instruments owned and pledged as collateral:
	Stocks		865,051			-			-			865,051
	Warrants		312			-			-			312
	U.S. and foreign government obligations		103,015			-			-			103,015
	Corporate and municipal bonds		1,998			-			-			1,998
	Total financial instruments owned and pledged as collateral		970,376			-			-			970,376

	Subtotal		4,379,056			46,036			181			4,425,273

	Other fair value investments, included in other assets:
	Stocks		7,545			407			-			7,952
	Corporate and municipal bonds		1,820			39,120			-			40,940
	Mortgage backed securities		-			28,081			-			28,081
	Other asset backed securities		-			14,607			-			14,607
	Other		-			8,717			-			8,717

	Total Financial Assets at Fair Value	$	6,889,048		$	136,968		$	181		$	7,026,197

			Financial Liabilities At Fair Value as of September 30, 2013

			Level 1			Level 2			Level 3			Total
	Financial instruments sold, not yet purchased:
	Stocks	$	1,443,990		$	-		$	64		$	1,444,054
	Options		2,058,289			9,084			-			2,067,373
	Warrants and discount certificates		1,640			-			-			1,640
	U.S. and foreign government obligations		-			1,229			-			1,229
	Corporate bonds		70,056			7,981			-			78,037
	Currency forward contracts		-			959			-			959
	Total financial instruments sold, not yet purchased	$	3,573,975		$	19,253		$	64		$	3,593,292


			Financial Assets At Fair Value as of December 31, 2012

			Level 1			Level 2			Level 3			Total

	Securities segregated for regulatory purposes	$	2,297,024		$	-		$	-		$	2,297,024
	Financial instruments owned:
	Stocks		887,031			-			-			887,031
	Options		2,388,173			-			-			2,388,173
	Warrants and discount certificates		147,317			-			-			147,317
	U.S. and foreign government obligations		30,087			-			-			30,087
	Corporate and municipal bonds		104,387			59,533			-			163,920
	Currency forward contracts		-			1,351			-			1,351
	Total financial instruments owned		3,556,995			60,884			-			3,617,879

	Financial instruments owned and pledged as collateral:
	Stocks		775,222			-			-			775,222
	Warrants		350			-			-			350
	U.S. and foreign government obligations		146,953			-			-			146,953
Corporate and municipal bonds		4,332			-			-			4,332
Total financial instruments owned and pledged as collateral		926,857			-			-			926,857

Subtotal		4,483,852			60,884			-			4,544,736

Other fair value investments, included in other assets:
Stocks		17,707			3,549			-			21,256
Corporate and municipal bonds		2,249			53,325			-			55,574
Mortgage backed securities		-			21,311			-			21,311
Other asset backed securities		-			17,023			-			17,023
Other		-			1,068			-			1,068

Total Financial Assets at Fair Value	$	6,800,832		$	157,160		$	-		$	6,957,992

		Financial Liabilities At Fair Value as of December 31, 2012

		Level 1			Level 2			Level 3			Total
Financial instruments sold, not yet purchased:
Stocks	$	1,787,741		$	-		$	-		$	1,787,741
Options		2,389,871			-			-			2,389,871
Warrants and discount certificates		2,104			-			-			2,104
U.S. and foreign government obligations		451			-			-			451
Corporate bonds		90,710			11,833			-			102,543
Currency forward contracts		-			3,550			-			3,550
Total financial instruments sold, not yet purchased	$	4,270,877		$	15,383		$	-		$	4,286,260
Level 3 Financial Assets and Financial Liabilities	'
			Delisted
			Securities
	Balance, January 1, 2013	$	-
	Total gains or losses (realized/unrealized)
	- Included in earnings		(184)
	Purchases, issuances and settlements		-
	Transfers in and/or out of Level 3		365

	Balance, September 30, 2013	$	181
	Financial liabilities – Level 3 activities:
			Delisted
			Securities
	Balance, January 1, 2013	$	-
	Total gains or losses (realized/unrealized)
	- Included in earnings		77
	Purchases, issuances and settlements		-
	Transfers in and/or out of Level 3		(13)

	Balance, September 30, 2013	$	64
Netting of Financial Assets and Financial Liabilities	'
			30-Sep-13
												Gross Amounts Not Offset in the
												Condensed Consolidated Statement of
												Financial Condition
					Gross Amounts			Net Amounts of
					Offset in the			Assets Presented in
					Condensed			the Condensed
		Gross Amounts of			Consolidated			Consolidated
		Recognized			Statement of			Statement of				Financial				Cash Collateral
		Assets			Financial Condition			Financial Condition				Instruments				Received			Net Amount
	Offsetting of Financial Assets:
	Securities segregated for regulatory purposes -
	purchased under agreements to resell	$	6,510.1	(1)	$	-		$	6,510.1		$	(6,510.1	)		$	-		$	-
	Securities borrowed		3,363.2			-			3,363.2			(3,363.2	)			-			-
	Securities purchased under agreements to resell		487.8			-			487.8			(487.8	)			-			-
	Financial Instruments owned:
	Options		2,139.4			-			2,139.4			(1,945.1	)			-			194.3
	Warrants and discount certificates		55.4			-			55.4			(1.6	)			-			53.8
	Currency forward contracts		4.2			-			4.2			-				-			4.2
	Total	$	12,560.1		$	-		$	12,560.1		$	(12,307.8	)		$	-		$	252.3





												Gross Amounts Not Offset in the
												Condensed Consolidated Statement of
												Financial Condition
					Gross Amounts			Net Amounts of
					Offset in the			Liabilities Presented
					Condensed			in the Condensed
		Gross Amounts of			Consolidated			Consolidated
		Recognized			Statement of			Statement of				Financial				Cash Collateral
		Liabilities			Financial Condition			Financial Condition				Instruments				Pledged			Net Amount
	Offsetting of Financial Liabilities:
	Securities loaned	$	2,193.0		$	-		$	2,193.0		$	(2,193.0	)		$	-		$	-
	Financial instruments sold, not yet purchased:
	Options		2,067.4			-			2,067.4			(1,945.1	)			-			122.3
	Warrants and discount certificates		1.6			-			1.6			(1.6	)			-			-
	Currency forward contracts		1.0			-			1.0			-				-			1.0
	Total	$	4,263.0		$	-		$	4,263.0		$	(4,139.7	)		$	-		$	123.3


			31-Dec-12
												Gross Amounts Not Offset in the
												Condensed Consolidated Statement of
												Financial Condition
					Gross Amounts			Net Amounts of
					Offset in the			Assets Presented in
					Condensed			the Condensed
		Gross Amounts of			Consolidated			Consolidated
		Recognized			Statement of			Statement of				Financial				Cash Collateral
		Assets			Financial Condition			Financial Condition				Instruments				Received			Net Amount
	Offsetting of Financial Assets:
	Securities segregated for regulatory purposes -
	purchased under agreements to resell	$	6,366.4	(1)	$	-		$	6,366.4		$	(6,366.4	)		$	-		$	-
	Securities borrowed		2,833.1			-			2,833.1			(2,833.1	)			-			-
	Securities purchased under agreements to resell		428.9			-			428.9			(428.9	)			-			-
	Financial Instruments owned:
	Options		2,388.2			-			2,388.2			(2,202.1	)			-			186.1
	Warrants and discount certificates		147.3			-			147.3			(2.1	)			-			145.2
	Currency forward contracts		1.4			-			1.4			-				-			1.4
	Total	$	12,165.3		$	-		$	12,165.3		$	(11,832.6	)		$	-		$	332.7





											Gross Amounts Not Offset in the
											Condensed Consolidated Statement of
											Financial Condition
				Gross Amounts			Net Amounts of
				Offset in the			Liabilities Presented
				Condensed			in the Condensed
	Gross Amounts of			Consolidated			Consolidated
	Recognized			Statement of			Statement of				Financial				Cash Collateral
	Liabilities			Financial Condition			Financial Condition				Instruments				Pledged			Net Amount
Offsetting of Financial Liabilities:
Securities loaned	$	1,839.3		$	-		$	1,839.3		$	(1,839.3	)		$	-		$	-
Financial instruments sold, not yet purchased:
Options		2,389.9			-			2,389.9			(2,202.1	)			-			187.8
Warrants and discount certificates		2.1			-			2.1			(2.1	)			-			-
Currency forward contracts		3.6			-			3.6			-				-			3.6
Total	$	4,234.9		$	-		$	4,234.9		$	(4,043.5	)		$	-		$	191.4

	-1	As of September 30, 2013 and December 31, 2012, the company had $6.51 billion and $6.37 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 unaudited condensed consolidated statements of financial condition.

Collateralized_Transactions_Ta

Collateralized Transactions (Tables)	3 Months Ended
Collateralized Transactions (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Amounts Related to Collateralized Transactions	'
		September 30, 2013				December 31, 2012 (2)

			Permitted		Sold or		Permitted		Sold or
			to Repledge		Repledged		to Repledge		Repledged

	Securities lending transactions	$	9,082.1	$	2,941.5	$	5,323.7	$	2,699.2
	Agreements to resell (1)		7,003.6		7,003.6		6,778.8		6,778.8
	Customer margin securities		10,304.0		3,609.2		13,603.7		3,016.3
		$	26,389.7	$	13,554.3	$	25,706.2	$	12,494.3

Financial instruments owned and pledged where the counterparty has the right to repledge	'
			September 30,		December 31,
			2013		2012
	Stocks	$	865.1	$	775.2
	Warrants		0.3		0.4
	U.S. and foreign government obligations		103.0		147.0
	Corporate and municipal bonds		2.0		4.3
		$	970.4	$	926.9

Defined_Contribution_and_Emplo1

Defined Contribution and Employee Incentive Plans (Tables)	3 Months Ended
Defined Contribution and Employee Incentive Plans (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
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
		17,284,454	$	302.4
2007 Stock Incentive Plan, ROI Summary	'
		Shares
		2007 Stock	2007 ROI Unit
		Incentive Plan	Stock Plan

	Balance, December 31, 2012	12,402,482	169,289

	Granted	-	-
	Forfeited	(308,925)	(6,423)
	Distributed (1)	(2,309,122)	(162,866)
	Balance, September 30, 2013	9,784,435	-

	(1) Shares distributed under the 2007 Stock Incentive Plan include 10,404 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.

Segment_and_Geographic_Informa1

Segment and Geographic Information (Tables)	3 Months Ended
Segment and Geographic Information (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Segment and geographic information	'
			Three months ended							Nine months ended
			September 30,							September 30,
			2013			2012				2013		2012
	Net revenues:
	Electronic brokerage	$	194.7		$	167.6			$	602.5	$	498.3
	Market making		130.9			154.1				221.9		387.8
	Corporate and eliminations		0.7			(3.1	)			1.9		(2.7	)
	Total net revenues	$	326.3		$	318.6			$	826.3	$	883.4

	Income before income taxes:
	Electronic brokerage	$	108.4		$	80.8			$	342.7	$	254.4
	Market making		87.5			90.2				66.1		180.2
	Corporate and eliminations		0.5			1.6				3.7		(3.8	)
	Total income before income taxes	$	196.4		$	172.6			$	412.5	$	430.8


			September 30,				December 31,
			2013				2012
	Assets:
	Electronic brokerage	$	29,612.5			$	25,741.5
	Market making		12,513.3				12,730.8
	Corporate and eliminations		(5,848.8	)			(5,272.7	)
	Total assets	$	36,277.0			$	33,199.6

			Three months ended							Nine months ended
			September 30,							September 30,
			2013			2012				2013		2012
	Net revenues:
	United States	$	265.4		$	237.1			$	597.3	$	645.4
	International		59.5			86.0				227.2		243.4
	Corporate and eliminations		1.4			(4.5	)			1.8		(5.4	)
	Total net revenues	$	326.3		$	318.6			$	826.3	$	883.4

	Income before income taxes:
	United States	$	180.9		$	134.1			$	331.9	$	348.0
	International		14.3			38.3				76.9		89.1
	Corporate and eliminations		1.2			0.2				3.7		(6.3	)
	Total income before income taxes	$	196.4		$	172.6			$	412.5	$	430.8

Regulatory_Requirements_Tables

Regulatory Requirements (Tables)	3 Months Ended
Regulatory Requirements (Tables)	Sep. 30, 2013
Notes to Consolidated Financial Statements	'
Regulatory requirements [table]	'
			Net Capital/
			Eligible Equity		Requirement		Excess
	IB LLC	$	1,922.0	$	283.0	$	1,639.0
	TH LLC		470.0		50.5		419.5
	THE		654.3		169.3		485.0
	Other regulated Operating Companies		404.7		34.0		370.7
		$	3,451.0	$	536.8	$	2,914.2

Recovered_Sheet1

Organization and Nature of Business (Detail)	Sep. 30, 2013	3-May-07
Organization and Nature of Business	'	'
IBG Inc. ownership % of IBG LLC	12.40%	10.00%

Significant_Accounting_Policie2

Significant Accounting Policies (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	3-May-07
Significant accounting policies	'	'	'
SIP expense - Year of grant	'	'	50.00%
SIP expense - Remaining vesting period	'	'	50.00%
SIP expense - Employees over fifty nine in year of grant	'	'	100.00%
Over 59 percent of shares eligible	'	'	100.00%
Percent of shares forfeited post employment	'	'	50.00%
U.S. Treasury Bills	$2,500,000	$2,297,000	'
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	6,510,000	6,370,000	'
Equity method investments	27,000	34,700	'
Cost method investments	$27,800	$36,200	'
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 Basic Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Basic earnings per share:	'	'	'	'
Net income attributable to common stockholders	$16,447	$12,488	$33,382	$31,556
Add (deduct) net income attributable to non-fair value redemption rights	0	0	0	1,108
Net income available for common stockholders	$16,447	$12,488	$33,382	$32,664
Weighted average shares of common stock outstanding:	'	'	'	'
Basic	49,966,050	47,488,459	48,807,321	46,588,213
Basic earnings per share	$0.33	$0.26	$0.68	$0.70
Common Class A	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Basic	49,965,950	47,488,359	48,807,221	46,588,113
Common Class B	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Basic	100	100	100	100

Equity_and_Earnings_Per_Share_2

Equity and Earnings Per Share Diluted Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Diluted earnings per share:	'	'	'	'
Net income available for common stockholders	$16,447	$12,488	$33,382	$32,664
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	49,966,050	47,488,459	48,807,321	46,588,213
Potentially dilutive common shares:	'	'	'	'
Issuable pursuant to 2007 ROI Unit Stock Plan	1,022,164	191,359	1,174,343	277,557
Weighted Average Number of Shares Outstanding, Diluted	50,988,214	47,679,818	49,981,664	46,865,770
Earnings Per Share, Diluted	$0.32	$0.26	$0.67	$0.70
Common Class A	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	49,965,950	47,488,359	48,807,221	46,588,113
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 Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended	12 Months Ended	36 Months Ended	77 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2013	Dec. 31, 2012	3-May-07
Equity and earnings per share	'	'	'	'	'	'	'	'	'
IBG Inc. ownership % of IBG LLC	12.40%	'	'	12.40%	'	'	12.40%	'	10.00%
IBG Holdings ownership % of IBG LLC	87.60%	'	'	87.60%	'	'	87.60%	'	90.00%
IBG Holdings Redemption of IBG LLC	'	'	'	'	'	'	'	'	10.00%
IBG Holdings LLC Owernship Percentage of Class B Common Stock	'	'	'	'	'	'	'	'	100.00%
Preferred stock shares authorized	10,000	'	'	10,000	'	'	10,000	10,000	'
Preferred stock shares issued	0	'	'	0	'	'	0	0	'
Preferred stock shares outstanding	0	'	'	0	'	'	0	0	'
Amortization period DTA (years)	15	'	'	15	'	'	15	15	'
Deferred tax asset from common stock offerings	$266,600	'	'	$266,600	'	'	$266,600	$281,615	'
Percent of Tax Savings Owed to IBG Holdings LLC	85.00%	'	'	85.00%	'	'	85.00%	'	'
Percentage of tax savings retained by IBG Inc.	15.00%	'	'	15.00%	'	'	15.00%	'	'
Deferred tax asset arising from Common Stock offerings	387,069	'	'	387,069	'	'	387,069	'	'
Tax savings owed to IBG Holdings LLC	329,009	'	'	329,009	'	'	329,009	'	'
Tax savings retained by IBG Inc.	58,060	'	'	58,060	'	'	58,060	'	'
Tax savings paid to IBG Holdings LLC	'	'	'	'	'	'	70,400	'	'
Exchange Agreement Future Redemption Schedule	'	'	'	'	'	'	'12.5% annually for seven (7) years and 2.5% in the eighth year.	'	'
Shares reserved for future issuance	'	'	'	'	'	'	'	'	360,000,000
Shares redeemed by IBG Holdings from IBG LLC	'	'	'	'	'	5,013,259	'	'	'
Cash Redemptions IBG Holdings	'	'	'	'	'	114,000	'	'	'
Shares Issued	'	'	'	'	1,983,624	'	'	'	'
Thomas Peterffy and Affiliates Ownership	86.40%	'	'	86.40%	'	'	86.40%	'	84.60%
Dividends paid by IBG LLC	'	'	'	122,700	'	'	'	'	'
Cash dividend paid to IBG, Inc.	$5,000	$5,000	$4,700	$15,000	'	'	'	'	'
Dividend per share	$0.10	$0.10	$0.10	'	'	'	'	'	'
Declaration Date	15-Oct-13	'	'	'	'	'	'	'	'
Record Date	29-Nov-13	'	'	'	'	'	'	'	'
Payment Date	13-Dec-13	'	'	'	'	'	'	'	'
Common Class A	'	'	'	'	'	'	'	'	'
Equity and earnings per share	'	'	'	'	'	'	'	'	'
Common stock, par value	$0.01	'	'	$0.01	'	'	$0.01	$0.01	'
Shares authorized	1,000,000,000	'	'	1,000,000,000	'	'	1,000,000,000	1,000,000,000	'
Common stock, shares issued	50,096,562	'	'	50,096,562	'	'	50,096,562	47,797,844	'
Common stock, shares outstanding	49,971,727	'	'	49,971,727	'	'	49,971,727	47,499,739	'
Common Class B	'	'	'	'	'	'	'	'	'
Equity and earnings per share	'	'	'	'	'	'	'	'	'
Common stock, par value	$0.01	'	'	$0.01	'	'	$0.01	$0.01	'
Shares authorized	100	'	'	100	'	'	100	100	'
Common stock, shares issued	100	'	'	100	'	'	100	100	'
Common stock, shares outstanding	100	'	'	100	'	'	100	100	'

Recovered_Sheet2

Equity And Earnings Per Share Adjustments (Detail) (USD $)	Jun. 06, 2012
In Thousands, unless otherwise specified	Jun. 06, 2012
Equity and earnings per share	'
Redeemable noncontrolling interests [Adjustment]	($5,367,553)
Additional Paid in Capital [Adjustment]	472,409
Retained earnings [Adjustment]	572,840
Noncontrolling interests [Adjustment]	$4,322,304

Comprehensive_Income_Table_Det

Comprehensive Income Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Comprehensive income	'	'	'	'
Comprehensive income attributable to common stockholders	$20,077	$14,382	$29,666	$32,370
Add (deduct) net income attributable to non-fair value redemption rights	0	0	0	1,108
Comprehensive income available for common stockholders	$20,077	$14,382	$29,666	$33,478
Earnings per share on comprehensive income:	'	'	'	'
Basic	$0.40	$0.30	$0.61	$0.72
Diluted	$0.39	$0.30	$0.59	$0.71
Weighted average common shares outstanding:	'	'	'	'
Basic	49,966,050	47,488,459	48,807,321	46,588,213
Diluted	50,988,214	47,679,818	49,981,664	46,865,770

Fair_Value_Table_Detail

Fair Value Table (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Securities segregated for regulatory purposes	$2,500,627	$2,297,024
Financial instruments owned	3,454,897	3,617,879
Financial instruments owned and pledged as collateral	970,376	926,857
Total financial instruments owned	4,425,273	4,544,736
Other investments	100,297	116,232
Total financial assets, at fair value	7,026,197	6,957,992
Financial instruments sold but not yet purchased, at fair value	3,593,292	4,286,260
Common Stock [Member]	'	'
Financial instruments owned	1,167,487	887,031
Financial instruments owned and pledged as collateral	865,051	775,222
Other investments	7,952	21,256
Financial instruments sold but not yet purchased, at fair value	1,444,054	1,787,741
Options [Member]	'	'
Financial instruments owned	2,139,384	2,388,173
Financial instruments sold but not yet purchased, at fair value	2,067,373	2,389,871
Warrants and discount certificates [Member]	'	'
Financial instruments owned	55,392	147,317
Financial instruments sold but not yet purchased, at fair value	1,640	2,104
U.S. and Foreign Government Obligations [Member]	'	'
Financial instruments owned	4,276	30,087
Financial instruments owned and pledged as collateral	103,015	146,953
Financial instruments sold but not yet purchased, at fair value	1,229	451
Warrants [Member]	'	'
Financial instruments owned and pledged as collateral	312	350
Corporate and municipal bonds [Member]	'	'
Financial instruments owned	84,205	163,920
Financial instruments owned and pledged as collateral	1,998	4,332
Other investments	40,940	55,574
Financial instruments sold but not yet purchased, at fair value	78,037	102,543
Mortgage Backed Securities [Member]	'	'
Other investments	28,081	21,311
Other Asset Backed Securities [Member]	'	'
Other investments	14,607	17,023
Currency forward contracts [Member]	'	'
Financial instruments owned	4,153	1,351
Financial instruments sold but not yet purchased, at fair value	959	3,550
Other assets - investments [Member]	'	'
Other investments	8,717	1,068
Level 1	'	'
Securities segregated for regulatory purposes	2,500,627	2,297,024
Financial instruments owned	3,408,680	3,556,995
Financial instruments owned and pledged as collateral	970,376	926,857
Total financial instruments owned	4,379,056	4,483,852
Other investments	9,365	19,956
Total financial assets, at fair value	6,889,048	6,800,832
Financial instruments sold but not yet purchased, at fair value	3,573,975	4,270,877
Level 1 \| Common Stock [Member]	'	'
Financial instruments owned	1,167,306	887,031
Financial instruments owned and pledged as collateral	865,051	775,222
Other investments	7,545	17,707
Financial instruments sold but not yet purchased, at fair value	1,443,990	1,787,741
Level 1 \| Options [Member]	'	'
Financial instruments owned	2,119,958	2,388,173
Financial instruments sold but not yet purchased, at fair value	2,058,289	2,389,871
Level 1 \| Warrants and discount certificates [Member]	'	'
Financial instruments owned	55,392	147,317
Financial instruments sold but not yet purchased, at fair value	1,640	2,104
Level 1 \| U.S. and Foreign Government Obligations [Member]	'	'
Financial instruments owned	1,967	30,087
Financial instruments owned and pledged as collateral	103,015	146,953
Financial instruments sold but not yet purchased, at fair value	0	451
Level 1 \| Warrants [Member]	'	'
Financial instruments owned and pledged as collateral	312	350
Level 1 \| Corporate and municipal bonds [Member]	'	'
Financial instruments owned	64,057	104,387
Financial instruments owned and pledged as collateral	1,998	4,332
Other investments	1,820	2,249
Financial instruments sold but not yet purchased, at fair value	70,056	90,710
Level 2	'	'
Financial instruments owned	46,036	60,884
Total financial instruments owned	46,036	60,884
Other investments	90,932	96,276
Total financial assets, at fair value	136,968	157,160
Financial instruments sold but not yet purchased, at fair value	19,253	15,383
Level 2 \| Common Stock [Member]	'	'
Other investments	407	3,549
Level 2 \| Options [Member]	'	'
Financial instruments owned	19,426	0
Financial instruments sold but not yet purchased, at fair value	9,084	0
Level 2 \| U.S. and Foreign Government Obligations [Member]	'	'
Financial instruments owned	2,309	0
Financial instruments sold but not yet purchased, at fair value	1,229	0
Level 2 \| Corporate and municipal bonds [Member]	'	'
Financial instruments owned	20,148	59,533
Other investments	39,120	53,325
Financial instruments sold but not yet purchased, at fair value	7,981	11,833
Level 2 \| Mortgage Backed Securities [Member]	'	'
Other investments	28,081	21,311
Level 2 \| Other Asset Backed Securities [Member]	'	'
Other investments	14,607	17,023
Level 2 \| Currency forward contracts [Member]	'	'
Financial instruments owned	4,153	1,351
Financial instruments sold but not yet purchased, at fair value	959	3,550
Level 2 \| Other assets - investments [Member]	'	'
Other investments	8,717	1,068
Level 3	'	'
Financial instruments owned	181	0
Total financial instruments owned	181	0
Total financial assets, at fair value	181	0
Financial instruments sold but not yet purchased, at fair value	64	0
Level 3 \| Common Stock [Member]	'	'
Financial instruments owned	181	0
Financial instruments sold but not yet purchased, at fair value	$64	$0

Netting_Financial_Assets_Detai

Netting Financial Assets (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Total [Domain]	'		'
Gross Amounts of Recognized Assets	$12,560,100		$12,165,300
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	12,560,100		12,165,300
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	-12,307,800		-11,832,600
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	252,300		332,700
Securities segregated for regulatory purposes - purchased under agreements to resell [Member]	'		'
Gross Amounts of Recognized Assets	6,510,100	[1]	6,366,400	[1]
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	6,510,100		6,366,400
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	-6,510,100		-6,366,400
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Securities Borrowed [Member]	'		'
Gross Amounts of Recognized Assets	3,363,200		2,833,100
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	3,363,200		2,833,100
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	-3,363,200		-2,833,100
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Securities Purchased Under Agreement to Resell [Member]	'		'
Gross Amounts of Recognized Assets	487,800		428,900
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	487,800		428,900
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	-487,800		-428,900
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Options owned [Member]	'		'
Gross Amounts of Recognized Assets	2,139,400		2,388,200
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	2,139,400		2,388,200
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	-1,945,100		-2,202,100
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	194,300		186,100
Warrants and discount certificates owned [Member]	'		'
Gross Amounts of Recognized Assets	55,400		147,300
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	55,400		147,300
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	-1,600		-2,100
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	53,800		145,200
Currency forward contracts owned [Member]	'		'
Gross Amounts of Recognized Assets	4,200		1,400
Gross Amounts Assets Offset in the Condensed Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	4,200		1,400
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Financial Instruments)	0		0
Gross Amounts of Assets Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	$4,200		$1,400

[1]	As of September 30, 2013 and December 31, 2012, the Company had $6.51 billion and $6.37 billion, respectively, of securities purchased under sgreements to resell that were segregated to satisfy regulatory requirements. These securities are included in "Cash and securities - segregated for regulatory purposes" in the unaudited condensed consolidated statements of financial condition.

Netting_Financial_Liabilities_

Netting Financial Liabilities (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Total [Domain]	'	'
Gross Amounts of Recognized Liabilities	$4,263,000	$4,234,900
Gross Amounts Liabilities Offset in the Condensed Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	4,263,000	4,234,900
Gross Amounts of Liabilities Not Offset in the Condensed Consolidated Satement of Financial Position (Financial Instruments)	-4,139,700	-4,043,500
Gross Amounts Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	123,300	191,400
Securities Loaned [Member]	'	'
Gross Amounts of Recognized Liabilities	2,193,000	1,839,300
Gross Amounts Liabilities Offset in the Condensed Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	2,193,000	1,839,300
Gross Amounts of Liabilities Not Offset in the Condensed Consolidated Satement of Financial Position (Financial Instruments)	-2,193,000	-1,839,300
Gross Amounts Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	0	0
Options Sold, Not Yet Purchased [Member]	'	'
Gross Amounts of Recognized Liabilities	2,067,400	2,389,900
Gross Amounts Liabilities Offset in the Condensed Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	2,067,400	2,389,900
Gross Amounts of Liabilities Not Offset in the Condensed Consolidated Satement of Financial Position (Financial Instruments)	-1,945,100	-2,202,100
Gross Amounts Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	122,300	187,800
Warrants and discount certificates sold, not yet purchased [Member]	'	'
Gross Amounts of Recognized Liabilities	1,600	2,100
Gross Amounts Liabilities Offset in the Condensed Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	1,600	2,100
Gross Amounts of Liabilities Not Offset in the Condensed Consolidated Satement of Financial Position (Financial Instruments)	-1,600	-2,100
Gross Amounts Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	0	0
Currency forward contracts sold, not yet purchased [Member]	'	'
Gross Amounts of Recognized Liabilities	1,000	3,600
Gross Amounts Liabilities Offset in the Condensed Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	1,000	3,600
Gross Amounts of Liabilities Not Offset in the Condensed Consolidated Satement of Financial Position (Financial Instruments)	0	0
Gross Amounts Not Offset in the Condensed Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	$1,000	$3,600

Level_3_Financial_Assets_Detai

Level 3 Financial Assets (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Financial Assets - Level 3 activities - Delisted Securities	'
Beginning balance	$0
Total gains or losses (realized/unrealized) - Included in earnings (Assets)	-184
Purchases, issuances and settlements (Assets)	0
Transfers in and/or out of Level 3 (Assets)	365
Ending balance	$181

Level_3_Financial_Liabilities_

Level 3 Financial Liabilities (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Financial liabilities - Level 3 - Delisted Securities	'
Beginning balance	$0
Total gains or losses (realized/unrealized) - Included in earnings (Liabilities)	77
Purchases, issuances and settlements (Liabilities)	0
Transfers in and/or out of Level 3 (Liabilities)	-13
Ending balance	$64

Fair_Value_Additional_Informat

Fair Value Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
[FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable]	'	'	'
Transfers of financial instruments owned from level 1 to level 2	$200	$1,700	'
Transfers of financial instruments owned from level 2 to level 1	200	1,400	'
Transfers of financial instruments sold, but not yet purchased from level 1 to level 2	500	1,300	'
Transfers of financial instruments sold, but not yet purchased from level 2 to level 1	600	1,500	'
Total financial assets, at fair value	7,026,197	7,026,197	6,957,992
Financial instruments sold but not yet purchased, at fair value	3,593,292	3,593,292	4,286,260
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	6,510,000	6,510,000	6,370,000
Level 3	'	'	'
[FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable]	'	'	'
Total financial assets, at fair value	181	181	0
Financial instruments sold but not yet purchased, at fair value	$64	$64	$0

Collateralized_Transactions_Ad

Collateralized Transactions Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Collateralized transactions [Abstract]	'	'
Customer margin loans outstanding	$12,727,552	$9,851,018
Securities repledged and deposited for customers	$6,510,000	$6,370,000
Percentage of securities repledged and deposited for customers	93.00%	94.00%

Collateralized_Transactions_Co

Collateralized Transactions Collateralized Table (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Permitted to Repledge	'	'
Securities lending transactions	$9,082,100	$5,323,700
Agreements to resell	7,003,600	6,778,800
Customer margin securities	10,304,000	13,603,700
Total collateralized transactions	26,389,700	25,706,200	[1]
Sold or Repledged	'	'
Securities lending transactions	2,941,500	2,699,200
Agreements to resell	7,003,600	6,778,800	[2]
Customer margin securities	3,609,200	3,016,300
Total collateralized transactions	$13,554,300	$12,494,300	[1]

[1]	The Company has revised its reporting of collateral permitted to be repledged and collateral sold or repledged, primarily with respect to securities available for repledging under securities lending transactions in connection with the Company's Stock Yield Enhancement Program. Disclosures for December 31, 2012 have been conformed to the new presentation for comparability purposes.
[2]	At September 30, 2013, $6.51 billion or 93% (at December 31, 2012, $6.37 billion, or 94%), 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_Ri

Collateralized Transactions Right to Repledge Table (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financial instruments owned and pledged where the counterparty has the right to repledge [Abstract]	'	'
Stocks	$865,100	$775,200
Warrants	300	400
Corporate and municipal bonds	2,000	4,300
U.S. and foreign government obligations	103,000	147,000
Financial Instruments Owned and Pledged as Collateral - Eligible to be Repledged by Counterparty	$970,400	$926,900

Senior_Notes_Payable_Detail

Senior Notes Payable (Detail) (USD $)	Dec. 31, 2011
In Thousands, unless otherwise specified	Dec. 31, 2011
Senior Notes Payable [Abstract]	'
Senior Notes at 3%	$101,411

Senior_Secured_Revolving_Credi1

Senior Secured Revolving Credit Facility (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	17-May-12
Senior Secured Revolving Credit Facility [Abstract]	'	'	'
Senior secured revolving credit facility maximum capacity	$100,000	'	$100,000
Minimum consolidated shareholders' equity	3,600,000	'	'
Quarterly Increases % of Positive Net Income	25.00%	'	'
Maximum debt to capitalization ratio	30.00%	'	'
Minimum liquidity ratio	'	'	'
Minimum liquidity ratio	minimum liquidity ratio of 1.0 to 1.0	'	'
Maximum debt to net regulatory capital ratio	35.00%	'	'
Outstanding debt under credit facility	$0	$0	'

Defined_Contribution_and_Emplo2

Defined Contribution and Employee Incentive Plan Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended			77 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012			Sep. 30, 2013	3-May-07	Dec. 31, 2006
Defined contribution and employee incentive plan additional information	'	'	'			'	'	'
ROI Dollar Unit Payable	$5,500	'	$7,600			$5,500	'	'
Vested balance of ROI payable	5,500	'	7,600			5,500	'	'
ROI dollar compensation expense	500	600	'			'	'	'
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	'	'	'			'	38,143	'
Vesting Percentage	'	'	'			'	'	'
				·	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 following six anniversaries of the first vesting, assuming continued employment with IBG, Inc. and compliance with non-competition and other applicable covenants.
Fair Value ROI Accrual	'	'	'			'	'	17,806
Compensation Expense, ROI Unit Stock Plan	'	2,700	'			'	'	'
Shares granted to external directors	'	'	'			20,423	'	'
2007 Stock Incentive Plan Compensation Expense	28,100	51,200	'			'	'	'
Estimated Future 2007 Stock Incentive Plan Compensation Expense	$30,200	'	'			$30,200	'	'
Over 59 percent of shares eligible	'	'	'			'	100.00%	'
Percent of shares forfeited post employment	'	'	'			'	50.00%	'
Former employees vesting schedule (Years)	'	'	'			'	5	'
Post employment vesting percentage (Years 1 - 4)	'	'	'			'	12.50%	'
Post employment vesting percentage (Year 5)	'	'	'			'	50.00%	'
Post employment shares distribution	'	'	'			78,312	'	'
2007 SIP shares issued under the ROI Unit Stock Plan that have been distributed	10,404	'	'			10,404	'	'

Recovered_Sheet3

Defined Contribution And Employee Incentive Plan Stock Plan Activity Table (Detail)	9 Months Ended
	Sep. 30, 2013
2007 Stock Incentive Plan (Shares)	'
Beginning Balance	12,402,482
Shares Granted	0
Shares Forfeited	-308,925
Shares Distributed	-2,309,122	[1]
Ending Balance	9,784,435
2007 ROI Unit Stock Plan (Shares)	'
Beginning Balance	169,289
Shares Granted	0
Shares Forfeited	-6,423
Shares Distributed	-162,866
Ending Balance	0

[1]	Shares distributed under the 2007 Stock Incentive Plan include 10,404 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.

Defined_Contribution_and_Emplo3

Defined Contribution and Employee Incentive Plan SIP Grants Table (Detail) (USD $)	77 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 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
SIP Share Grants	'	'	'	'	'	'	'	'	'	'
Shares granted	'	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)	'	$50,500	$18,400	$50,800	$43,200	$42,800	$35,600	$32,900	$400	$27,800
Shares Granted IPO to Date	17,284,454	'	'	'	'	'	'	'	'	'
Fair Value - Date of Grant ($000's) IPO to Date	$302,400	'	'	'	'	'	'	'	'	'

Income_Taxes_Additional_Inform

Income Taxes Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Income Taxes [Abstract]	'	'
Undistributed accumulated earnings of foreign subsidiaries	$1,060,000	$969,800
Accumulated earnings of foreign pass through subsidiaries	416,700	380,600
Accumulated earnings subject to additional foreign tax	$315,500	$297,500

Segment_and_Geographic_Informa2

Segment and Geographic Information Segment Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Net revenues	$326,252	$318,599	$826,282	$883,409	'
Income before income taxes	196,382	172,620	412,531	430,804	'
Assets	36,277,044	'	36,277,044	'	33,199,557
Electronic brokerage	'	'	'	'	'
Net revenues	194,700	167,571	602,500	498,250	'
Income before income taxes	108,400	80,735	342,700	254,358	'
Assets	29,612,500	'	29,612,500	'	25,741,495
Market making	'	'	'	'	'
Net revenues	130,900	154,140	221,900	387,824	'
Income before income taxes	87,500	90,230	66,100	180,203	'
Assets	12,513,300	'	12,513,300	'	12,730,811
Corporate and eliminations	'	'	'	'	'
Net revenues	700	-3,112	1,900	-2,665	'
Income before income taxes	500	1,655	3,700	-3,757	'
Assets	($5,848,800)	'	($5,848,800)	'	($5,272,749)

Segment_and_Geographic_Informa3

Segment and Geographic Information Geographic Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net revenues	$326,252	$318,599	$826,282	$883,409
Income before income taxes	196,382	172,620	412,531	430,804
United States	'	'	'	'
Net revenues	265,400	237,123	597,300	645,399
Income before income taxes	180,900	134,055	331,900	348,001
International	'	'	'	'
Net revenues	59,500	85,994	227,200	243,389
Income before income taxes	14,300	38,257	76,900	89,089
Geographic corporate and eliminations	'	'	'	'
Net revenues	1,400	-4,518	1,800	-5,379
Income before income taxes	$1,200	$200	$3,700	($6,286)

Regulatory_Requirements_Table_

Regulatory Requirements Table (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified	Sep. 30, 2013
All Operating Companies	'
Excess regulatory capital	$2,914,200
Net Capital / Eligible Equity	3,451,000
Required net capital	536,800
IB LLC	'
Excess regulatory capital	1,639,000
Net Capital / Eligible Equity	1,922,000
Required net capital	283,100
TH LLC	'
Excess regulatory capital	419,500
Net Capital / Eligible Equity	470,000
Required net capital	50,500
THE	'
Excess regulatory capital	485,000
Net Capital / Eligible Equity	654,300
Required net capital	169,300
Other regulated operating companies	'
Excess regulatory capital	370,700
Net Capital / Eligible Equity	404,700
Required net capital	$34,000

Regulatory_Requirements_Additi

Regulatory Requirements Additional Information (Detail) (All Operating Companies, USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified	Sep. 30, 2013
All Operating Companies	'
Excess regulatory capital	$2,914,200

Related_Party_Transactions_Det

Related Party Transactions (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Related Party	'	'
Due from Related Parties - Customers	$14,300	$1,100
Due to Related Parties - Customers	$268,800	$745,000

Subsequent_Events_Detail

Subsequent Events (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified	Sep. 30, 2013
Subsequent Events	'
Reduction in Market Value	90.00%
Current Margin Deficit	$68,000
Maximum Possible Margin Deficit Loss	$84,000