Interactive Brokers (IBKR) 10-Q 11 Aug 14 2014 Q2 Quarterly report Financial data

Documentation_and_Entity_Infor

Documentation and Entity Information	6 Months Ended
	Jun. 30, 2014	Aug. 11, 2014	Aug. 11, 2014
		Common Class A	Common Class B
Entity Registrant Name	'Interactive Brokers Group, Inc.	'	'
Entity Central Index Key	'0001381197	'	'
Document Type	'10-Q	'	'
Document Period End Date	30-Jun-14	'	'
Amendment Flag	'false	'	'
Fiscal Year Focus	'2014	'	'
Fiscal Period Focus	'Q2	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Common Stock Shares Outstanding	'	57,098,889	100

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Financial Condition (Unaudited) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets	'	'
Cash and cash equivalents	$999,630	$1,213,241
Cash and securities - segregated for regulatory purposes	15,520,061	13,991,711
Securities borrowed	3,499,241	2,751,501
Securities purchased under agreements to resell	274,321	386,316
Financial instruments owned, at fair value:	'	'
Financial instruments owned	2,398,625	3,285,313
Financial instruments owned and pledged as collateral	839,467	1,163,531
Total financial instruments owned	3,238,092	4,448,844
Receivables:	'	'
Customers, less allowance for doubtful accounts of $7,591 and $67,999 at June 30, 2014 and December 31, 2013	15,326,943	13,596,650
Brokers, dealers and clearing organizations	765,337	858,189
Receivable from affiliate	'	55
Interest	32,680	26,489
Total receivables	16,124,960	14,481,383
Other assets	499,194	597,704
Total assets	40,155,499	37,870,700
Liabilities and equity	'	'
Financial instruments sold but not yet purchased, at fair value	2,630,785	3,153,673
Securities loaned	2,932,404	2,563,653
Short-term borrowings	15,193	24,635
Payables:	'	'
Customers	28,411,102	26,319,420
Brokers, dealers and clearing organizations	382,252	330,956
Payable to affiliate	271,467	287,242
Accounts payable, accrued expenses and other liabilities	232,398	96,026
Interest	4,307	2,969
Total payables	29,301,526	27,036,613
Total liabilities	34,879,908	32,778,574
Stockholders' equity:	'	'
Additional paid-in capital	613,386	583,312
Retained earnings	121,942	98,868
Accumulated other comprehensive income, net of income taxes of $1,121 and $936 at June 30, 2014 and December 31, 2013	28,874	27,028
Treasury stock, at cost, 121,570 and 123,954 shares at June 30, 2014 and December 31, 2013	-2,420	-2,492
Total stockholders' equity	762,354	707,264
Noncontrolling interests	4,513,237	4,384,862
Total equity	5,275,591	5,092,126
Total liabilities and stockholders' equity	40,155,499	37,870,700
Common Class A	'	'
Stockholders' equity:	'	'
Common stock	572	548
Common Class B	'	'
Stockholders' equity:	'	'
Common stock	$0	$0

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Financial Condition (Unaudited) (Parenthetical) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Allowance for doubtful accounts	$7,591	$67,999
Common stock, par value	$0.01	$0.01
Accumulated Other Comprehensive Income, Tax	$1,121	$936
Treasury stock shares	121,570	123,954
Common Class A	'	'
Shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	57,220,459	54,788,049
Common stock, shares outstanding	57,098,889	54,664,095
Common Class B	'	'
Shares authorized	100	100
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues:	'	'	'	'
Trading gains	$84,020	$59,106	$211,532	$78,100
Commissions and execution fees	124,351	138,092	260,992	257,630
Interest income	95,027	76,070	180,910	146,572
Other income	17,843	24,262	37,001	44,173
Total revenues	321,241	297,530	690,435	526,475
Interest expense	11,942	13,574	26,228	26,445
Total net revenues	309,299	283,956	664,207	500,030
Non-interest expenses:	'	'	'	'
Execution and clearing	51,634	64,727	105,844	124,267
Employee compensation and benefits	53,589	58,018	107,075	104,336
Occupancy, depreciation and amortization	9,693	9,249	19,512	19,318
Communications	6,185	5,703	12,187	11,156
General and administrative	13,989	12,333	27,236	24,804
Total non-interest expenses	135,090	150,030	271,854	283,881
Income before income taxes	174,209	133,926	392,353	216,149
Income tax expense	13,451	13,890	30,401	20,825
Net income	160,758	120,036	361,952	195,324
Less net income attributable to noncontrolling interests	145,597	109,658	327,702	178,389
Net income available for common stockholders	15,161	10,378	34,250	16,935
Earnings per share:	'	'	'	'
Basic	$0.27	$0.21	$0.62	$0.35
Diluted	$0.26	$0.21	$0.60	$0.35
Weighted average common shares outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	56,079,813	48,929,348	55,375,929	48,218,572
Weighted Average Number of Shares Outstanding, Diluted	57,300,230	49,012,567	56,674,666	48,354,098
Comprehensive income:	'	'	'	'
Net income available for common stockholders	15,161	10,378	34,250	16,935
Other comprehensive income:	'	'	'	'
Cumulative translation adjustment, before income taxes	1,539	-4,007	2,030	-7,742
Income taxes related to items of other comprehensive income	61	-403	184	-396
Other comprehensive income (loss), net of tax	1,478	-3,604	1,846	-7,346
Comprehensive income available for common stockholders	16,639	6,774	36,096	9,589
Comprehensive income attributable to noncontrolling interests:	'	'	'	'
Net income attributable to noncontrolling interests	145,597	109,658	327,702	178,389
Other comprehensive income (loss) - cumulative translation adjustment	9,552	-27,994	12,672	-55,615
Comprehensive income attributable to noncontrolling interests	$155,149	$81,664	$340,374	$122,774

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Cash flows from operating activities:	'	'
Net income	$361,952	$195,324
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Deferred income taxes	8,447	9,350
Depreciation and amortization	9,451	9,439
Employee stock plan compensation	21,601	24,181
Losses (gains) on other investments, net	3,509	-636
Bad debt expense	1,013	1,343
Change in operating assets and liabilities:	'	'
Increase in cash and securities - segregated for regulatory purposes	-1,526,993	-230,065
Increase in securities borrowed	-747,740	-433,869
Decrease (increase) in securities purchased under agreements to resell	111,995	-158,665
Decrease in financial instruments owned	1,210,691	132,064
Increase in receivables from customers	-1,731,306	-1,460,788
Decrease (increase) in other receivables	86,715	-105,839
Increase in other assets	-10,902	-23,000
Decrease in financial instruments sold but not yet purchased	-522,888	-245,110
Increase in securities loaned	368,751	629,029
Increase in payable to customers	2,091,682	1,532,913
Increase (decrease) in other payables	60,248	-47,984
Net cash used in operating activities	-203,774	-172,313
Cash flows from investing activities:	'	'
Purchases of other investments	-74,073	-126,870
Proceeds from sales of other investments	298,060	159,838
Distributions received from and redemptions of equity investments	1,074	11,054
Purchase of property and equipment	-9,544	-7,946
Net cash provided by investing activities	215,517	36,076
Cash flows from financing activities:	'	'
Dividends paid to stockholders	-11,176	-9,745
Distributions to noncontrolling interests	-203,502	-70,406
Decrease in short-term borrowings, net	-9,442	-97,594
Payments made under the Tax Receivable Agreement	-15,752	'
Net cash used in financing activities	-239,872	-177,745
Effect of exchange rate changes on cash and cash equivalents	14,518	-62,961
Net decrease in cash and cash equivalents	-213,611	-376,943
Cash and cash equivalents at beginning of period	1,213,241	1,380,599
Cash and cash equivalents at end of period	999,630	1,003,656
Supplemental disclosures of cash flow information:	'	'
Cash paid for interest	24,890	28,816
Cash paid for taxes	20,826	36,973
Non-cash financing activities:	'	'
Adjustments to additional paid-in capital for changes in proportionate ownership in IBG LLC	27,132	19,826
Adjustments to noncontrolling interests for changes in proportionate ownership in IBG LLC	($27,132)	($19,826)

Condensed_Consolidated_Stateme4

Condensed Consolidated Statements of Changes in Equity (Unaudited) (USD $)	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Total Stockholders' Equity [Member]	Non-controlling Interests [Member]	Total
In Thousands, except Share data
Balance at Dec. 31, 2012	$478	$493,912	($7,718)	$82,072	$29,754	$598,498	$4,214,649	$4,813,147
Common stock, shares issued at Dec. 31, 2012	47,797,844	'	'	'	'	'	'	'
Common stock distributed pursuant to stock plans	22	-22	5,184	'	'	5,184	'	5,184
Common Stock distributed pursuant to stock plans (in shares)	2,292,992	'	'	'	'	'	'	'
Compensation for stock grants vesting in the future	'	2,964	'	'	'	2,964	21,621	24,585
Dividends paid to stockholders	'	'	'	-9,745	'	-9,745	'	-9,745
Distributions from IBG LLC to noncontrolling interests	'	'	'	'	'	'	-70,406	-70,406
Adjustments for changes in proportionate ownership in IBG LLC	'	19,826	'	'	'	19,826	-19,826	'
Comprehensive Income	'	'	'	16,935	-7,346	9,589	122,774	132,363
Balance at Jun. 30, 2013	500	516,680	-2,534	89,262	22,408	626,316	4,268,812	4,895,128
Common stock, shares issued at Jun. 30, 2013	50,090,836	'	'	'	'	'	'	'
Balance at Dec. 31, 2013	548	583,312	-2,492	98,868	27,028	707,264	4,384,862	5,092,126
Common stock, shares issued at Dec. 31, 2013	54,788,049	'	'	'	'	'	'	'
Common stock distributed pursuant to stock plans	24	-24	72	'	'	72	'	72
Common Stock distributed pursuant to stock plans (in shares)	2,432,410	'	'	'	'	'	'	'
Compensation for stock grants vesting in the future	'	2,966	'	'	'	2,966	18,635	21,601
Dividends paid to stockholders	'	'	'	-11,176	'	-11,176	'	-11,176
Distributions from IBG LLC to noncontrolling interests	'	'	'	'	'	'	-203,502	-203,502
Adjustments for changes in proportionate ownership in IBG LLC	'	27,132	'	'	'	27,132	-27,132	'
Comprehensive Income	'	'	'	34,250	1,846	36,096	340,374	376,470
Balance at Jun. 30, 2014	$572	$613,386	($2,420)	$121,942	$28,874	$762,354	$4,513,237	$5,275,591
Common stock, shares issued at Jun. 30, 2014	57,220,459	'	'	'	'	'	'	'

Organization_And_Nature_Of_Bus

Organization And Nature Of Business	6 Months Ended
	Jun. 30, 2014
Organization And Nature Of Business [Abstract]	'
Organization And Nature Of Business	'
	1. Organization and Nature of Business
	Interactive Brokers Group, Inc. (“IBG, Inc.” or the “Company”) is a Delaware holding company whose primary asset is its ownership of approximately 14.1% of the membership interests of IBG LLC, which, in turn, owns operating subsidiaries (collectively, “IBG LLC” or the “Group”). The accompanying 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”):  Interactive Brokers LLC (“IB LLC”) and subsidiary (Interactive Brokers Corp.), Interactive Brokers Canada Inc. (“IBC”), Interactive Brokers (U.K.) Limited (“IBUK”), Interactive Brokers Securities Japan, Inc. (“IBSJ”), Interactive Brokers (India) Private Limited (“IBI”),  Timber Hill LLC (“TH LLC”), Timber Hill Europe AG and subsidiary (collectively “THE”), Timber Hill Securities Hong Kong Limited (“THSHK”), Timber Hill Australia Pty Limited (“THA”), Timber Hill Canada Company (“THC”), Interactive Brokers Financial Products S.A. (“IBFP”), Interactive Brokers Hungary KFT (“IBH”), IB Exchange Corp. (“IBEC”), Interactive Brokers Software Services Estonia OU (“IBEST”) and Interactive Brokers Software Services Russia (“IBRUS”).
	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 13). IB LLC, IBUK, IBC, IBI and IBSJ carry securities accounts for customers or perform custodial functions relating to customer securities.

Significant_Accounting_Policie

Significant Accounting Policies	6 Months Ended
	Jun. 30, 2014
Significant Accounting Policies [Abstract]	'
Significant Accounting Policies	'
	2. Significant Accounting Policies
	Basis of Presentation
	These condensed consolidated financial statements are presented in U.S. dollars and have been prepared 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 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 June 30, 2014 and December 31, 2013, the results of operations and comprehensive income for the six months ended June 30, 2014 and 2013 and cash flows for the six months ended June 30, 2014 and 2013. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in IBG, Inc.’s 2013 Annual Report on Form 10-K filed with the SEC on March 3, 2014. The condensed consolidated financial statement information as of December 31, 2013 has been derived from the 2013 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 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 financial statements and records the interests in the Group that IBG, Inc. does not own as noncontrolling interests.
	The Company’s policy is to consolidate all other entities in which it owns more than 50% unless it does not have control. All inter‑company balances and transactions have been eliminated.
	Use of Estimates
	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in the 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 allowance for doubtful accounts, compensation accruals, current and deferred income taxes, and estimated contingency reserves.
	Fair Value
	Substantially all of IBG, Inc.’s assets and liabilities, including financial instruments are carried at fair value based on published market prices and are marked to market, or are assets and liabilities which are short‑term in nature and are carried at amounts that approximate fair value.
	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, 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.
	Other fair value investments, reported in other assets in the accompanying condensed consolidated statement of financial condition and in Note 6—Financial Assets and Financial Liabilities, are comprised of financial instruments that the Company does not carry in its market making business, which were comprised of listed stocks and options, and corporate debt securities.  These investments are generally reported as Level 2 financial instruments, except for unrestricted listed equities, which are classified as Level 1 financial instruments.  Other fair value liabilities are comprised of unrestricted listed equities which are classified as Level 1 financial instruments.
	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.
	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 condensed consolidated financial statements using a fair value‑based method. Grants, which are denominated in U.S. dollars, are communicated to employees in the year of grant, thereby establishing the fair value of each grant. The fair value of awards granted to employees are generally expensed as follows—50% in the year of grant in recognition of plan forfeiture provisions (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 stock‑based compensation plans are subject to forfeiture in the event an employee ceases employment with the Company. The plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted.
	Cash and Cash Equivalents
	The Company considers all highly liquid investments, with maturities of three months or less, that are not segregated and deposited for regulatory purposes or to meet margin requirements at clearing houses to be cash equivalents.
	Cash and Securities—Segregated for Regulatory Purposes
	As a result of customer activities, certain Operating Companies are obligated by rules mandated by their primary regulators to segregate or set aside cash or qualified securities to satisfy such regulations, which regulations have been promulgated to protect customer assets. 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 $3.43 billion and $1.30 billion at June 30, 2014 and December 31, 2013, respectively, which are recorded as Level 1 financial assets and securities purchased under agreements to resell in the amount of $5.91 billion and $6.73 billion as of June 30, 2014 and December 31, 2013, respectively, which amounts approximate fair value.
	Securities Borrowed and Securities Loaned
	Securities borrowed and securities loaned are recorded at the amount of 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 condensed consolidated statements of financial condition.
	Securities lending fees received or paid by IBG, Inc. are recorded as interest income or interest expense in the condensed consolidated statements of comprehensive income.
	Securities Purchased Under Agreements to Resell
	Securities purchased under agreements to resell, which are reported as collateralized financing transactions, are recorded at contract value, plus accrued interest, which approximates fair value. To ensure that the fair value of the underlying collateral remains sufficient, 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 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 condensed consolidated statements of financial condition.
	Customer Receivables and Payables
	Customer securities transactions are recorded on a settlement date basis and customer commodities transactions are recorded on a trade date basis. Receivables from and payables to customers include amounts due on cash and margin transactions, including futures contracts transacted on behalf of customers. Securities owned by customers, including those that collateralize margin loans or other similar transactions, are not reported in the condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are expensed 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 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 condensed consolidated statements of comprehensive income. The recorded amounts of IBG, Inc.’s equity method investments, $24.7 million at June 30, 2014 ($27.5 million at December 31, 2013), which are reported as a component of other assets in the 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 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, $27.5 million at June 30, 2014 ($27.6 million at December 31, 2013), are recorded at cost or, if an other‑than‑temporary impairment in value has occurred, at a value that reflects management’s estimate of the impairment, and are also components of other assets in the condensed consolidated statements of financial condition. Dividends received from cost basis investments are recognized as a component of other income when 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 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. In general, the practice and intention of the Company is to reinvest the earnings of its non‑U.S. subsidiaries in those operations.
	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.
	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. Included in trading gains are net gains and losses on exchange traded options, futures and other derivative instruments. Dividends are integral to the valuation of stocks and interest is integral to the valuation of fixed income instruments. Accordingly, both dividends and interest income and expense attributable to financial instruments owned and financial instruments sold but not yet purchased are reported on a net basis as a component of trading gains in the accompanying 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 condensed consolidated statements of comprehensive income, and the related expenses are reported as execution and clearing expenses.
	—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 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 10) 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.
	IBG, Inc. recognizes interest related to income tax matters as interest income or expense and penalties related to income tax matters as income tax expense.
	Deferred income tax assets and liabilities arise from temporary differences between the tax and financial 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. The Company is not aware of any such changes that would have a material effect on the Company’s results of operations, cash flows, or financial position.
ASC 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 2014, prior to the issuance of the Company’s condensed consolidated financial statements, ASUs 2014-01 through 2014-14 have been issued. Following is a summary of recently issued ASUs that have affected or may affect the Company’s condensed consolidated financial statements:
		Affects	Status
ASU 2013-05		Foreign Currency Matters (Topic 830): Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity	Effective for fiscal periods beginning on or after December 15, 2013.
ASU 2014-06		Technical Corrections and Improvements Related to Glossary Terms	Effective on issuance in March 2014.
ASU 2014-09		Revenue from Contracts with Customers (Topic 606)	Effective for fiscal periods beginning on or after December 15, 2016.
ASU 2014-11		Transfers and Servicing (Topic 860): Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures.	Effective for the first interim or annual period beginning after December 15, 2014.
Adoption of those ASUs that became effective during 2014, prior to the issuance of the Company’s condensed consolidated financial statements, did not have a material effect on those financial statements.

Trading_Activities_And_Related

Trading Activities And Related Risks	6 Months Ended
	Jun. 30, 2014
Trading Activities And Related Risks [Abstract]	'
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. The Company manages this risk using spot (i.e., cash) currency transactions, currency futures contracts and currency forward contracts.
	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, and 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. Repos are collateralized by securities with a market value in excess of the obligation under the contract. Similarly, securities lending agreements are collateralized by deposits of cash or securities. 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 June 30, 2014, the Company did not have any material concentrations of credit risk.
	Off‑Balance Sheet Risks
	IBG, Inc. may be exposed to a risk of loss not reflected in the condensed consolidated financial statements to settle futures and certain over‑the‑counter contracts at contracted prices, which may require repurchase or sale of the underlying products in the market at prevailing prices. Accordingly, these transactions result in off‑balance sheet risk as IBG, Inc.’s cost to liquidate such contracts may exceed the amounts reported in IBG, Inc.’s condensed consolidated statements of financial condition.

Equity_And_Earnings_Per_Share

Equity And Earnings Per Share	6 Months Ended
	Jun. 30, 2014
Equity And Earnings Per Share [Abstract]	'
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 85.9% as of June 30, 2014.  The condensed consolidated financial statements reflect the results of operations and financial position of IBG, Inc., including consolidation of its investment in IBG LLC. 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 June 30, 2014 and December 31, 2013, 1,000,000,000 shares of Class A common stock were authorized, of which 57,220,459 and 54,788,049 shares have been issued; and 57,098,889 and 54,664,095 shares were outstanding, respectively. Class B common stock is comprised of 100 authorized shares, of which 100 shares were issued and outstanding as of June 30, 2014 and December 31, 2013, respectively. In addition, 10,000 shares of preferred stock have been authorized, of which no shares are issued or outstanding as of June 30, 2014 and December 31, 2013, 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 and 2013 redemptions of Holdings member interests in exchange for common stock, which deferred tax assets are a component of other assets in the 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 and 2013 redemption dates, respectively, as allowable under current tax law. As of June 30, 2014 and December 31, 2013, the unamortized balance of these deferred tax assets was $283.5 million and $294.7 million, respectively.
	IBG, Inc. also entered into an agreement (the “Tax Receivable Agreement”) with Holdings to pay Holdings (for the benefit of the former members of IBG LLC) 85% of the tax savings that IBG, Inc. actually realizes as the result of tax basis increases. These payables, net of payments made to Holdings, are reported as payable to affiliate in the condensed consolidated statement of financial condition.
	The remaining 15% is accounted for as a permanent increase to additional paid‑in capital in the 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 June 30, 2014 were $420.4 million, $357.4 million and $63.1 million, respectively. Amounts payable under the Tax Receivable Agreement are payable to Holdings annually following the filing of IBG, Inc.’s federal income tax return. The Company has paid Holdings a cumulative total of $86.2 million of which $15.7 million was paid in the six months ended June 30, 2014, pursuant to the terms of the Tax Receivable Agreement.
	The Exchange Agreement, as amended June 6, 2012, provides for future redemptions of member interests and for the purchase of member interests in IBG LLC by IBG, Inc. from Holdings, which could result in IBG, Inc. acquiring the remaining member interests in IBG LLC that it does not own. On an annual basis, holders of Holdings member interests are able to request redemption of such member interests over a minimum eight (8) year period following the IPO; 12.5% annually for seven (7) years and 2.5% in the eighth year.
	At the time of the 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 2013 and 2011, respectively, the Company issued 4,683,415 shares and 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 9), IBG, Inc.’s interest in IBG LLC has increased to approximately 14.1%, with Holdings owning the remaining 85.9% as of June 30, 2014. The redemptions also resulted in an increase in the Holdings interest held by Thomas Peterffy and his affiliates from approximately 84.6% at the IPO to approximately 87.6% at June 30, 2014.
	Earnings per Share
	Basic earnings per share are calculated utilizing net income available for common stockholders divided by the weighted average number of shares of Class A and Class B common stock outstanding for that period:
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Basic earnings per share:
	Net income available for common stockholders	$	15,161	$	10,378	$	34,250	$	16,935
	Weighted average shares of common stock outstanding:
	Class A		56,079,713		48,929,248		55,375,829		48,218,472
	Class B		100		100		100		100
			56,079,813		48,929,348		55,375,929		48,218,572
	Basic earnings per share	$	0.27	$	0.21	$	0.62	$	0.35
	Diluted earnings per share are calculated utilizing the Company’s basic net income available for common stockholders divided by diluted weighted average shares outstanding with no adjustments to net income available to common stockholders for potentially dilutive common shares:
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Diluted earnings per share:
	Net income available for common stockholders	$	15,161	$	10,378	$	34,250	$	16,935
	Weighted average shares of common stock outstanding:
	Class A:
	Issued and outstanding		56,079,713		48,929,248		55,375,829		48,218,472
	Potentially dilutive common shares issuable pursuant to employee incentive plans		1,220,417		83,219		1,298,737		135,526
	Class B		100		100		100		100
			57,300,230		49,012,567		56,674,666		48,354,098
	Diluted earnings per share	$	0.26	$	0.21	$	0.60	$	0.35
	Member Distributions and Stockholder Dividends
	For the six months ended June 30, 2014, IBG LLC made distributions totaling $235.8 million to its members, of which IBG, Inc.’s proportionate share was $32.3 million.  In March and June 2014, the Company paid cash dividends of $0.10 per share of Common Stock, totaling $5.5 million and $5.7 million, respectively.
	On July15, 2014, the Company declared a cash dividend of $0.10 per common share, payable on September 12, 2014 to shareholders of record as of August 29, 2014.

Comprehensive_Income

Comprehensive Income	6 Months Ended
	Jun. 30, 2014
Comprehensive Income Detail [Abstract]	'
Comprehensive Income	'
	5. Comprehensive Income
	The following table presents comprehensive income and earnings per share on comprehensive income:
		Three months ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Comprehensive income available for common stockholders, net of tax	$	16,639	$	6,774	$	36,096	$	9,589
	Earnings per share on comprehensive income:
	Basic	$	0.30	$	0.14	$	0.65	$	0.20
	Diluted	$	0.29	$	0.14	$	0.64	$	0.20
	Weighted average common shares outstanding:
	Basic		56,079,813		48,929,348		55,375,929		48,218,572
	Diluted		57,300,230		49,012,567		56,674,666		48,354,098

Financial_Assets_And_Financial

Financial Assets And Financial Liabilities	6 Months Ended
	Jun. 30, 2014
Financial Assets And Financial Liabilities [Abstract]	'
Financial Assets And Financial Liabilities	'
	6. Financial Assets and Financial Liabilities
	Fair Value
	The following tables set forth, by level within the fair value hierarchy (Note 2), financial assets and liabilities, primarily financial instruments owned and financial instruments sold, but not yet purchased at fair value as of June 30, 2014 and December 31, 2013. 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 June 30, 2014
			Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes		$	3,427,880		$	-		$	-		$	3,427,880
	Financial instruments owned:
	Stocks			1,151,367			-			260			1,151,627
	Options			1,072,980			-			-			1,072,980
	Warrants and discount certificates			34,345			-			-			34,345
	U.S. and foreign government securities			16,049			3,866			-			19,915
	Corporate and municipal bonds			91,243			19,920			-			111,163
	Currency forward contracts			-			8,595			-			8,595
	Total financial instruments owned			2,365,984			32,381			260			2,398,625
	Financial instruments owned and pledged as collateral:
	Stocks			759,705			-			-			759,705
	Warrants			273			-			-			273
	U.S. and foreign government securities			78,012			-			-			78,012
	Corporate and municipal bonds			1,477			-			-			1,477
	Total financial instruments owned and pledged as collateral			839,467			-			-			839,467
	Total financial insturments owned			3,205,451			32,381			260			3,238,092
	Other fair value investments, included in other assets:
	Stocks and options			33,159			-			106			33,265
	Corporate and municipal bonds			-			1,696			-			1,696
	Total other fair value investments, included in other assets			33,159			1,696			106			34,961
	Total Financial Assets at Fair Value		$	6,666,490		$	34,077		$	366		$	6,700,933
			Financial Liabilities At Fair Value as of June 30, 2014
			Level 1			Level 2			Level 3			Total
	Financial instruments sold, not yet purchased:
	Stocks		$	1,370,830		$	-		$	77		$	1,370,907
	Options			1,168,783			-			-			1,168,783
	Warrants and discount certificates			603			-			-			603
	U.S. and foreign government securities			1,840			1,049			-			2,889
	Corporate bonds			77,047			10,556			-			87,603
	Currency forward contracts			-			-			-			-
	Total financial instruments sold, not yet purchased			2,619,103			11,605			77			2,630,785
	Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities
	Stocks and options			132,036			-			-			132,036
	Total other fair value liabilities, included in accounts payable, accrued expenses and other liabilities			132,036			-			-			132,036
	Total Financial Liabilities at Fair Value		$	2,751,139		$	11,605		$	77		$	2,762,821
				Financial Assets At Fair Value as of December 31, 2013
				Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes			$	1,300,016		$	-		$	-		$	1,300,016
	Financial instruments owned:
	Stocks				1,243,914			-			57			1,243,971
	Options				1,880,481			-			-			1,880,481
	Warrants and discount certificates				57,144			-			-			57,144
	U.S. and foreign government securities				4,641			2,102			-			6,743
	Corporate and municipal bonds				72,750			18,476			-			91,226
	Currency forward contracts				-			5,748			-			5,748
	Total financial instruments owned				3,258,930			26,326			57			3,285,313
	Financial instruments owned and pledged as collateral:
	Stocks				1,097,734			-			-			1,097,734
	Warrants				233			-			-			233
	U.S. and foreign government securities				64,439			-			-			64,439
	Corporate and municipal bonds				1,125			-			-			1,125
	Total financial instruments owned and pledged as collateral				1,163,531			-			-			1,163,531
	Total financial instruments owned				4,422,461			26,326			57			4,448,844
	Other fair value investments, included in other assets:
	Stocks				25,604			419			101			26,124
	Corporate and municipal bonds				1,776			47,896			-			49,672
	Mortgage backed securities				-			26,892			-			26,892
	Other asset backed securities				-			22,734			-			22,734
Other				-			5,328			-			5,328
Total other fair value assets				27,380			103,269			101			130,750
Total Financial Assets at Fair Value			$	5,749,857		$	129,595		$	158		$	5,879,610
		Financial Liabilities At Fair Value as of December 31, 2013
		Level 1			Level 2			Level 3			Total
Financial instruments sold, not yet purchased:
Stocks		$	1,266,429		$	-		$	3		$	1,266,432
Options			1,793,248			-			-			1,793,248
Warrants and discount certificates			1,215			-			-			1,215
U.S. and foreign government securities			-			4,412			-			4,412
Corporate bonds			77,936			9,628			-			87,564
Currency forward contracts			-			802			-			802
Total financial instruments sold, not yet purchased		$	3,138,828		$	14,842		$	3		$	3,153,673
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 six months ended June 30, 2014, the Company reclassified approximately $0.7 million of financial instruments owned from Level 1 to Level 2 and reclassified approximately $1.5 million from Level 2 to Level 1. Financial instruments sold, but not yet purchased of approximately $1.4 million were reclassified from Level 1 to Level 2 and approximately $4.5 million were reclassified from Level 2 to Level 1. The Company reclassified approximately $1.7 million of other fair value investments, recorded in other assets, from Level 1 to Level 2.
During the six months ended June 30, 2013, the Company reclassified approximately $1.9 million of financial instruments owned from Level 1 to Level 2 and reclassified approximately $1.6 million from Level 2 to Level 1.  Financial instruments sold, but not yet purchased of approximately $0.8 million were reclassified from Level 1 to Level 2 and approximately $0.9 million were reclassified from Level 2 to Level 1.
Level 3 Financial Assets and Financial Liabilities
The Company’s Level 3 financial assets and financial liabilities are comprised of delisted securities reported within financial instruments owned and financial instruments sold, not yet purchased. The following tables report Level 3 activities for the three months ended June 30, 2014:
Financial assets—Level 3 activities:
Balance, January 1, 2014		$	158
Total gains or losses (realized/unrealized)  - Included in earnings			43
Purchases, issuances and settlements			-38
Transfers in and/or out of Level 3			203
Balance, June 30, 2014		$	366
Financial liabilities—Level 3 activities:
Balance, January 1, 2014		$	3
Total gains or losses (realized/unrealized) - Included in earnings			-
Purchases, issuances and settlements			-
Transfers in and/or out of Level 3			74
Balance, June 30, 2014		$	77
There were no Level 3 activities, including transfers, for the six months ended June 30, 2013.
Trading Gains from Market Making Transactions
Trading gains, net from market making transactions reported in the statements of comprehensive income, by major product type, are comprised of:
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
Equities		$	56,564		$	92,992		$	151,709		$	161,516
Fixed Income			6,361			6,703			12,091			14,471
Foreign Exchange			21,095			-40,677			47,732			-98,002
Commodities			-			88			-			115
Total Trading Gains		$	84,020		$	59,106		$	211,532		$	78,100
These transactions are related to the Company’s financial instruments owned and financial instruments sold, not yet purchased (all at fair value) and include both derivative and non‑derivative financial instruments, including exchange traded options and futures. These gains and losses also include market making related dividend and fixed income trading interest income and expense.
The gains (losses) in the above table are not representative of the integrated trading strategies applied by the Company, which utilize financial instruments across various product types. Gains and losses in one product type frequently offset gains and losses in other product types.
Netting of Financial Assets and Financial Liabilities
The Company adopted the guidance in ASU 2011‑11, Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities and 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 does not net securities segregated for regulatory purposes, and securities borrowed and securities loaned are presented on a gross basis in the condensed consolidated statements of financial condition. In the tables below, the amounts of derivative financial instruments owned that are not offset in the condensed consolidated statements of financial condition, but could be netted against financial liabilities with specific counterparties under master netting agreements, including clearing houses (exchange traded options, warrants and discount certificates) or over the counter currency forward contract counterparties, are presented to provide financial statement readers with the Company’s estimate of its net exposure to counterparties for these derivative financial instruments.
The following table sets forth the netting of financial assets and of financial liabilities as of June 30, 2014 and December 31, 2013, pursuant to the requirements of ASU 2011‑11 and ASU 2013‑01 (millions).
		30-Jun-14
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
Offsetting of Financial Assets:
Securities segregated for regulatory purposes -purchased under agreements to resell		$	5,913.9	1		$	-		$	5,913.9		$	-5,913.90	$	-	$	-
Securities borrowed			3,499.2				-			3,499.2			-3,419.00		-		80.2
Securities purchased under agreements to resell			274.3				-			274.3			-274.3		-		-
Financial Instruments owned:			-										-
Options			1,073.0				-			1,073.0			-1,032.50		-		40.5
Warrants and discount certificates			34.6				-			34.6			-0.6		-		34.0
Currency forward contracts			8.6				-			8.6			-		-		8.6
Total		$	10,803.6			$	-		$	10,803.6		$	-10,640.30	$	-	$	163.3
									Net Amounts of			Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
Offsetting of Financial Liabilities:
Securities loaned		$	2,932.4			$	-		$	2,932.4		$	-2,932.00	$	-	$	0.4
Financial instruments sold, not yet purchased:
Options			1,168.8				-			1,168.8			-1,032.50		-		136.3
Warrants and discount certificates			0.6				-			0.6			-0.6		-		-
Currency forward contracts			-				-			-			-		-		-
Total		$	4,101.8			$	-		$	4,101.8		$	-3,965.10	$	-	$	136.7
		31-Dec-13
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
Offsetting of Financial Assets:
Securities segregated for regulatory purposes - purchased under agreements to resell		$	6,734.2	1		$	-		$	6,734.2		$	-6,734.20	$	-	$	-
Securities borrowed			2,751.5				-			2,751.5			-2,694.60		-		56.9
Securities purchased under agreements to resell			386.3				-			386.3			-386.3		-		-
Financial Instruments owned:
Options			1,880.5				-			1,880.5			-1,652.80		-		227.7
Warrants and discount certificates			57.4				-			57.4			-1.2		-		56.2
Currency forward contracts			5.7				-			5.7			-		-		5.7
Total		$	11,815.6			$	-		$	11,815.6		$	-11,469.10	$	-	$	346.5
									Net Amounts of				Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
Offsetting of Financial Liabilities:
Securities loaned		$	2,563.7			$	-		$	2,563.7		$	-2,544.60	$	-	$	19.1
Financial instruments sold, not yet purchased:
Options			1,793.2				-			1,793.2			-1,652.80		-		140.4
Warrants and discount certificates			1.2				-			1.2			-1.2		-		-
Currency forward contracts			0.8				-			0.8			-		-		0.8
Total		$	4,358.9			$	-		$	4,358.9		$	-4,198.60	$	-	$	160.3
	-1		As of June 30, 2014 and December 31, 2013, the Company had $5.91 billion and $6.73 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in “Cash and securities—segregated for regulatory purposes” in the condensed consolidated statements of financial condition.

Collateralized_Transactions

Collateralized Transactions	6 Months Ended
	Jun. 30, 2014
Disclosure Collateralized Transactions [Abstract]	'
Collateralized Transactions	'
	7. Collateralized Transactions
	The Company enters into securities borrowing and lending transactions and agreements to repurchase and resell securities to finance trading inventory, to obtain securities for settlement and to earn residual interest rate spreads. In addition, the Company’s customers pledge their securities owned to collateralize margin loans. Under these transactions, the Company either receives or provides collateral, including equity, corporate debt and U.S. government securities. Under many agreements, the Company is permitted to sell or repledge securities received as collateral and use these securities to secure 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 to customers on a demand basis and are not committed facilities. Factors considered in the acceptance or rejection of margin loans are the amount of the loan, the degree of leverage being employed in the customer account and an overall evaluation of the customer’s portfolio to ensure proper diversification or, in the case of concentrated positions, appropriate liquidity of the underlying collateral. Additionally, transactions relating to concentrated or restricted positions are limited or prohibited by raising the level of required margin collateral (to 100% in the extreme case). Underlying collateral for margin loans is evaluated with respect to the liquidity of the collateral positions, valuation of securities, volatility analysis and an evaluation of industry concentrations. Adherence to the Company’s collateral policies significantly limits the Company’s credit exposure to margin loans in the event of a customer’s default. Under margin lending agreements, the Company may request additional margin collateral from customers and may sell securities that have not been paid for or purchase securities sold but not delivered from customers, if necessary. At June 30, 2014 and December 31, 2013, approximately $15.33 billion and $13.60 billion, respectively, of customer margin loans were outstanding.
	Amounts relating to collateralized transactions at June 30, 2014 and December 31, 2013 are summarized as follows (millions):
			30-Jun-14				31-Dec-13
			Permitted		Sold or		Permitted		Sold or
			to Repledge		Repledged		to Repledge		Repledged
	Securities lending transactions		$	10,023.5	$	3,170.3	$	9,331.9	$	2,504.3
	Agreements to resell 1			6,187.0		6,183.8		7,116.1		7,099.6
	Customer margin assets			14,122.6		5,564.4		11,753.3		4,602.9
			$	30,333.1	$	14,918.5	$	28,201.3	$	14,206.8
		-1		At June 30, 2014, $5.91 billion or 96% (at December 31, 2013, $6.73 billion, or 95%, of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.
	In the normal course of business, the Company pledges qualified securities with clearing organizations to satisfy daily margin and clearing fund requirements. At June 30, 2014 and December 31, 2013, the majority of the Company’s government securities 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 June 30, 2014 and December 31, 2013 consisted of the following (millions):
			June 30,		December 31,
			2014		2013
	Stocks		$	759.7	$	1,097.8
	Warrants			0.3		0.2
	U.S. and foreign government obligations			78.0		64.4
	Corporate and municipal bonds			1.5		1.1
			$	839.5	$	1,163.5

Senior_Secured_Revolving_Credi

Senior Secured Revolving Credit Facility	6 Months Ended
	Jun. 30, 2014
Senior Secured Revolving Credit Facility [Abstract]	'
Senior Secured Revolving Credit Facility	'
	8. Senior Secured Revolving Credit Facility
	On May 17, 2012, IBG LLC entered into a $100 million three‑year senior secured revolving credit facility with Bank of America, N.A. as administrative agent and Citibank, N.A., as syndication agent. This credit facility replaced a similar two‑year facility that expired on May 18, 2012.  On August 8, 2014 the Group elected to terminate this credit facility.
	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 June 30, 2014 and December 31, 2013, 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.

Employee_Incentive_Plans

Employee Incentive Plans	6 Months Ended
	Jun. 30, 2014
Employee Incentive Plans [Abstract]	'
Employee Incentive Plans	'
	9. Employee Incentive Plans
	Return on Investment Dollar Units (“ROI Dollar Units”)
	From 1998 through January 1, 2006, IBG LLC granted all non‑member employees ROI Dollar Units, which are redeemable under the amended provisions of the plan, and in accordance with regulations issued by the Internal Revenue Service (Section 409A of the Internal Revenue Code). Upon redemption, the grantee is entitled to accumulated earnings on the face value of the certificate, but not the actual face value. For grants made in 1998 and 1999, grantees may redeem the ROI Dollar Units after vesting on the fifth anniversary of the date of their grant and prior to the tenth anniversary of the date of their grant. For grants made between January 1, 2000 and January 1, 2005, grantees must elect to redeem the ROI Dollar Units upon the fifth, seventh or tenth anniversary date. These ROI Dollar Units have vested at the fifth anniversary of the date of their grant and will continue to accumulate earnings until the elected redemption date. For grants made on or after January 1, 2006, all ROI Dollar Units vested on the fifth anniversary date of their grant and were or will be automatically redeemed. Subsequent to the IPO, no additional ROI Dollar Units have been or will be granted, and non‑cash compensation to employees will consist primarily of grants of shares of Common Stock as described below under “2007 Stock Incentive Plan.”
	As of June 30, 2014 and December 31, 2013, payables to employees for ROI Dollar Units were $3.1 million and $5.6 million, respectively, all of which were vested. These amounts are included in accounts payable, accrued expenses and other liabilities in the condensed consolidated statements of financial condition. Compensation expense for the ROI Dollar Unit plan, included in the condensed consolidated statements of comprehensive income was $0.3 million and $0.2 million for the six months ended June 30, 2014 and 2013, 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
	As of December 31, 2012, compensation costs for the ROI Unit Stock Plan had been fully accrued and as of December 31, 2013, all shares issued to current employees under the ROI Unit Stock Plan had been distributed.
	2007 Stock Incentive Plan
	Under the Interactive Brokers Group, Inc. 2007 Stock Incentive Plan (the “Stock Incentive Plan” or “SIP”), up to 30 million shares (20 million shares at December 31, 2013) of common stock may be granted and issued to directors, officers, employees, contractors and consultants of IBG, Inc. and its subsidiaries.  The 10 million increase in shares allocated to the SIP was approved by the Company’s Compensation Committee and Board of Directors in February 2014.  The Board of Directors’ approval was ratified by a vote of the stockholders at the Company’s 2014 Annual Meeting on April 24, 2014.  The purpose of the Stock Incentive Plan is to promote IBG, Inc.’s long‑term financial success by attracting, retaining and rewarding eligible participants.
	As a result of the Company’s organizational structure, a description of which can be found on page 4 of the Company’s 2013 Annual Report on Form 10-K, filed with the SEC, there is no dilutive effect upon ownership of minority shareholders of issuing shares under the Stock Incentive Plan.  The issuances do not dilute the book value of the ownership of minority shareholders because a) the restricted stock units are granted at market value and b) upon their vesting and the related issuance of shares of Common Stock, the ownership of the Company in its operating subsidiary, IBG LLC, increases proportionately to the shares issued. As a result of such proportionate increase in share ownership, the dilution upon issuance of Common Stock is borne by IBG LLC’s majority shareholder (i.e., noncontrolling interest), IBG Holdings LLC, and not by the Company or its minority shareholders. Additionally, dilution of earnings that may take place after issuance of Common Stock is reflected in the earnings per share (“EPS”) reported in the Company’s financial statements. The EPS dilution can be neither estimated nor projected, but historically it has not been material.
	The Stock Incentive Plan is administered by the Compensation Committee of 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 stock awards, including the number of awards granted to each employee and all other terms and conditions applicable to such awards in individual grant agreements. Awards are expected to be made primarily through grants of restricted Common Stock. Stock Incentive Plan awards are subject to issuance over time and may be forfeited upon an employee’s termination of employment or violation of certain applicable covenants prior to issuance, unless determined otherwise by the Compensation Committee.
	The Stock Incentive Plan provides that, upon a change in control, the Compensation Committee may, at its discretion, fully vest any granted but not yet earned awards under the Stock Incentive Plan, or provide that any such granted but not yet earned awards will be honored or assumed, or new rights substituted therefore by the new employer on a substantially similar basis and on terms and conditions substantially comparable to those of the Stock Incentive Plan.
	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. A total of 20,423 shares have been granted to the external directors cumulatively since the IPO.
	Stock Incentive Plan share grants (excluding 21,009 shares issued pursuant to the 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
	31-Dec-13		1,894,046			46.2
			19,178,500		$	348.6
	Estimated future grants under the Stock Incentive Plan are accrued for ratably during each year (Note 2).  In accordance with the vesting schedule, outstanding awards vest and are distributed to participants once each year on or about the Company’s IPO anniversary. At the end of each year, there are no vested awards that remain undistributed.
	Compensation expense recognized in the condensed consolidated statements of comprehensive income was $21.6 million and $24.1 million for the six months ended June 30, 2014 and 2013, respectively. Estimated future compensation costs for unvested awards at June 30, 2014 are $32.5 million.
	The following is a summary of stock plan activity for the six months ended June 30, 2014:
			Shares
			2007 Stock
			Incentive Plan
	Balance, December 31, 2013		11,647,117
	Granted		-
	Forfeited		-143,185
	Distributed (1)		-2,434,794
	Balance, June 30, 2014		9,069,138
		-1		Shares cumulatively distributed under the 2007 Stock Incentive Plan include 16,238 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.
	Awards granted under the stock plans are subject to forfeiture in the event an employee ceases employment with the Company. The stock plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted. Distributions of remaining awards granted on or before January 1, 2009 to former employees will occur within 90 days of the anniversary of the termination of employment date over a five (5) year vesting schedule, 12.5% in each of the first four years and 50% in the fifth year. Distributions of remaining awards granted on or after January 1, 2010 to former employees will occur over the remaining vesting schedule applicable to each grant. Through June 30, 2014, a total of 173,457 shares have been distributed under these post‑employment provisions. These distributions are included in the Stock Plans activity tables above.

Income_Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2014
Income Taxes [Abstract]	'
Income Taxes	'
	10. Income Taxes
	Income tax expense for the six months ended June 30, 2014 and 2013 differs from the U.S. federal statutory rate primarily due to the taxation treatment of income attributable to noncontrolling interests in IBG LLC.  These noncontrolling interests are subject to U.S. taxation as partnerships.  Accordingly, the income attributable to these noncontrolling interests is reported in the condensed consolidated statements of comprehensive income, but the related U.S. income tax expense attributable to these noncontrolling interests is not reported by the Company as it is the obligation of the individual partners.  Income tax expense is also affected by the differing effective tax rates in foreign, state and local jurisdictions where certain of the Company’s subsidiaries are subject to corporate taxation.
	Deferred income taxes arise primarily due to the amortization of the deferred tax assets recognized in connection with the Common Stock offerings (Note 4), differences in the valuation of financial assets and liabilities, and for other temporary differences arising from the deductibility of compensation and depreciation expenses in different time periods for book and income tax return purposes.
	As of and for the six months ended June 30, 2014 and 2013, the Company had no unrecognized tax liabilities as defined under ASC 740, Income Taxes and no valuation allowances on deferred tax assets were required. The Company is subject to taxation in the United States and various states and foreign jurisdictions. As of June 30, 2014, the Company is open to U.S. Federal and State income tax examinations for the tax years 2010 through 2012, and to non U.S. income tax examinations for the tax years 2006 through 2013.
	At June 30, 2014, accumulated earnings held by non‑U.S. subsidiaries totaled $1,082.9 million (at December 31, 2013 $1,072.9 million). Of this amount, approximately $405.6 million (at December 31, 2013 $422.3 million) is attributable to earnings of the Company’s foreign subsidiaries that are considered “pass‑through” entities for U.S. income tax purposes. Since the Company accounts for U.S. income taxes on these earnings on a current basis, no additional U.S. tax consequences would result from the repatriation of these earnings other than that which would be due arising from currency fluctuations between the time the earnings are reported for U.S. tax purposes and when they are remitted. With respect to certain of these subsidiaries’ accumulated earnings (approximately $303.7 million and $318.7 million as of June 30, 2014 and December 31, 2013, respectively), repatriation would result in additional foreign taxes in the form of dividend withholding tax imposed on the recipient of the distribution or dividend distribution tax imposed on the payor of the distribution. The Company has not provided for its proportionate share of these additional foreign taxes as it does not intend to repatriate these earnings in the foreseeable future. For the same reason, the Company has not provided deferred U.S. tax on cumulative translation adjustments associated with these earnings.
	The remainder of the accumulated earnings are attributable to non‑U.S. subsidiaries that are not considered “pass‑through” entities for U.S. tax purposes.  The Company’s U.S. tax basis in the stock of most of these entities exceeds its book basis. Establishing a deferred tax asset pursuant to ASC 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	6 Months Ended
	Jun. 30, 2014
Commitments, Contingencies And Guarantees [Abstract]	'
Commitments, Contingencies And Guarantees	'
	11. Commitments, Contingencies and Guarantees
	In October 2013, a small number of the Company’s brokerage customers had taken relatively large positions in four stocks listed on the Singapore Exchange. In early October, within a very short timeframe, these securities lost over 90% of their value. The customer accounts were margined and fell into deficits totaling $64 million prior to the time the Company took possession of their securities positions. The Company has recognized a cumulative loss of approximately $79.2 million from October 2013 through June 30, 2014. The maximum aggregate loss, which would occur if the securities’ prices all fell to zero and none of the debts were collected, would be approximately $84 million. The Company is currently pursuing the collection of the debts. The ultimate effect of this incident on the Company’s results will depend upon market conditions and the outcome of the Company’s debt collection efforts.
	Litigation
	The Company is subject to certain pending and threatened legal actions which arise out of the normal course of business. Litigation is inherently unpredictable, particularly in proceedings where claimants seek substantial or indeterminate damages, or which are in their early stages. 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 June 30, 2014 and December 31, 2013, reserves provided for potential losses related to litigation matters were not material.
	Guarantees
	Certain of the Operating Companies provide guarantees to securities clearing houses and exchanges which meet the accounting definition of a guarantee under 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 condensed consolidated statements of financial condition for these arrangements.
	In connection with its retail brokerage business, IB LLC or other electronic brokerage Operating Companies perform securities and commodities execution, clearance and settlement on behalf of their customers for whom they commit to settle trades submitted by such customers with the respective clearing houses. If a customer fails to fulfill its settlement obligations, the respective Operating Company must fulfill those settlement obligations. No contingent liability is carried on the condensed consolidated statements of financial condition for such customer obligations.
	Other Commitments
	Certain clearing houses and clearing banks and firms used by certain Operating Companies are given a security interest in certain assets of those Operating Companies held by those clearing organizations. These assets may be applied to satisfy the obligations of those Operating Companies to the respective clearing organizations.

Segment_And_Geographic_Informa

Segment And Geographic Information	6 Months Ended
	Jun. 30, 2014
Segment And Geographic Information [Abstract]	'
Segment And Geographic Information	'
	12. Segment and Geographic Information
	IBG, Inc. operates in two business segments: electronic brokerage and market making. IBG, Inc. conducts its electronic brokerage business through its Interactive Brokers subsidiaries, which provide electronic execution and clearing services to customers worldwide. The Company conducts its market making business principally through its Timber Hill subsidiaries on the world’s leading exchanges and market centers, primarily in exchange‑traded equities, equity options and equity‑index options and futures.
	Significant transactions and balances between the Operating Companies occur, primarily as a result of certain Operating Companies holding exchange or clearing organization memberships, which are utilized to provide execution and clearing services to affiliates. Charges for transactions between segments are designed to approximate full costs.  Intra‑segment and intra‑region income and expenses and related balances have been eliminated in this segment and geographic information to reflect the external business conducted in each segment or geographical region. Corporate items include non‑allocated corporate income and expenses that are not attributed to segments for performance measurement, corporate assets and eliminations.
	Management believes that the following information by business segment provides a reasonable representation of each segment’s contribution to total net revenues and income before income taxes for the three months ended June 30, 2014 and 2013, and to total assets as of June 30, 2014 and December 31, 2013 (millions):
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Net revenues:
	Electronic brokerage	$	220.6	$	212.5	$	444.3	$	407.8
	Market making		91.9		67.4		225.0		91.0
	Corporate and eliminations		-3.2		4.0		-5.1		1.2
	Total net revenues	$	309.3	$	283.9	$	664.2	$	500.0
	Income before income taxes:
	Electronic brokerage	$	131.4	$	123.3	$	265.7	$	234.3
	Market making		46.5		7.6		134.6		-21.4
	Corporate and eliminations		-3.7		3.0		-8		3.2
	Total income before income taxes	$	174.2	$	133.9	$	392.3	$	216.1
		June 30,		December 31,
		2014		2013
	Assets:
	Electronic brokerage	$	34,560.6	$	31,333.5
	Market making		12,190.7		12,139.5
	Corporate and eliminations		-6,595.80		-5,602.30
	Total assets	$	40,155.5	$	37,870.7
	The Company operates its automated global business in U.S. and international markets on more than 100 exchanges and market centers. A significant portion of 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 24 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 months ended June 30, 2014 and 2013 (millions):
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Net revenues:
	United States	$	252.5	$	193.4	$	535.3	$	331.9
	International		60.5		87.4		134.8		167.7
	Corporate and eliminations		-3.7		3.1		-5.9		0.4
	Total net revenues	$	309.3	$	283.9	$	664.2	$	500.0
	Income before income taxes:
	United States	$	165.1	$	99.0	$	362.1	$	151.0
	International		13.1		32.7		38.8		62.6
	Corporate and eliminations		-4		2.2		-8.6		2.5
	Total income before income taxes	$	174.2	$	133.9	$	392.3	$	216.1

Regulatory_Requirements

Regulatory Requirements	6 Months Ended
	Jun. 30, 2014
Regulatory Requirements [Abstract]	'
Regulatory Requirements	'
	13. Regulatory Requirements
	At June 30, 2014, aggregate excess regulatory capital for all of the Operating Companies was $3.23 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  Capital Requirements Directive, IBI is subject to the National Stock Exchange of India net capital requirements and IBSJ is subject to the Japanese Financial Supervisory Agency capital requirements. The following table summarizes capital, capital requirements and excess regulatory capital (millions):
		Net Capital/
		Eligible Equity		Requirement		Excess
	IB LLC	$	2,262.1	$	332.6	$	1,929.5
	TH LLC		436.0		60.3		375.7
	THE		706.8		197.2		509.6
	Other regulated Operating Companies		465.3		47.1		418.2
		$	3,870.2	$	637.2	$	3,233.0
	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 June 30, 2014, all of the regulated Operating Companies were in compliance with their respective regulatory capital requirements.

Related_Party_Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	14. Related Party Transactions
	Receivable from affiliate represents amounts advanced to Holdings and payable to affiliate represents amounts payable to Holdings under the Tax Receivable Agreement (Note 4).
	Included in receivables from and payables to customers in the accompanying  condensed consolidated statements of financial condition as of June 30, 2014 and December 31, 2013 were accounts receivable from directors, officers and their affiliates of $1.8 million and $0.4 million and payables of $409.8 million and $815.5 million, respectively.

Subsequent_Events

Subsequent Events	6 Months Ended
	Jun. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Events	'
	15. Subsequent Events
	As required by ASC 855, Subsequent Events, the Company has evaluated subsequent events for adjustment to or disclosure in its condensed consolidated financial statements through the date the condensed consolidated financial statements were issued.
	No recordable or disclosable events, not otherwise reported in these financial statements or the notes thereto, occurred.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2014
Significant Accounting Policies [Abstract]	'
Basis Of Presentation	'
	Basis of Presentation
	These condensed consolidated financial statements are presented in U.S. dollars and have been prepared 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 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 June 30, 2014 and December 31, 2013, the results of operations and comprehensive income for the six months ended June 30, 2014 and 2013 and cash flows for the six months ended June 30, 2014 and 2013. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in IBG, Inc.’s 2013 Annual Report on Form 10-K filed with the SEC on March 3, 2014. The condensed consolidated financial statement information as of December 31, 2013 has been derived from the 2013 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	'
	Principles of Consolidation, including Noncontrolling Interests
	The 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 financial statements and records the interests in the Group that IBG, Inc. does not own as noncontrolling interests.
	The Company’s policy is to consolidate all other entities in which it owns more than 50% unless it does not have control. All inter‑company balances and transactions have been eliminated.
Use Of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in the 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 allowance for doubtful accounts, compensation accruals, current and deferred income taxes, and estimated contingency reserves.
Fair Value	'
	Fair Value
	Substantially all of IBG, Inc.’s assets and liabilities, including financial instruments are carried at fair value based on published market prices and are marked to market, or are assets and liabilities which are short‑term in nature and are carried at amounts that approximate fair value.
	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, 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.
	Other fair value investments, reported in other assets in the accompanying condensed consolidated statement of financial condition and in Note 6—Financial Assets and Financial Liabilities, are comprised of financial instruments that the Company does not carry in its market making business, which were comprised of listed stocks and options, and corporate debt securities.  These investments are generally reported as Level 2 financial instruments, except for unrestricted listed equities, which are classified as Level 1 financial instruments.  Other fair value liabilities are comprised of unrestricted listed equities which are classified as Level 1 financial instruments.
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.
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 condensed consolidated financial statements using a fair value‑based method. Grants, which are denominated in U.S. dollars, are communicated to employees in the year of grant, thereby establishing the fair value of each grant. The fair value of awards granted to employees are generally expensed as follows—50% in the year of grant in recognition of plan forfeiture provisions (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 stock‑based compensation plans are subject to forfeiture in the event an employee ceases employment with the Company. The plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted.
Cash And Cash Equivalents	'
	Cash and Cash Equivalents
	The Company considers all highly liquid investments, with maturities of three months or less, that are not segregated and deposited for regulatory purposes or to meet margin requirements at clearing houses to be cash equivalents.
Cash And Securities - Segregated For Regulatory Purposes	'
	Cash and Securities—Segregated for Regulatory Purposes
	As a result of customer activities, certain Operating Companies are obligated by rules mandated by their primary regulators to segregate or set aside cash or qualified securities to satisfy such regulations, which regulations have been promulgated to protect customer assets. 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 $3.43 billion and $1.30 billion at June 30, 2014 and December 31, 2013, respectively, which are recorded as Level 1 financial assets and securities purchased under agreements to resell in the amount of $5.91 billion and $6.73 billion as of June 30, 2014 and December 31, 2013, respectively, which amounts approximate fair value.
Securities Borrowed And Securities Loaned	'
	Securities Borrowed and Securities Loaned
	Securities borrowed and securities loaned are recorded at the amount of 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 condensed consolidated statements of financial condition.
	Securities lending fees received or paid by IBG, Inc. are recorded as interest income or interest expense in the condensed consolidated statements of comprehensive income.
Securities Purchased Under Agreements To Resell	'
	Securities Purchased Under Agreements to Resell
	Securities purchased under agreements to resell, which are reported as collateralized financing transactions, are recorded at contract value, plus accrued interest, which approximates fair value. To ensure that the fair value of the underlying collateral remains sufficient, 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 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 condensed consolidated statements of financial condition.
Customer Receivables And Payables	'
	Customer Receivables and Payables
	Customer securities transactions are recorded on a settlement date basis and customer commodities transactions are recorded on a trade date basis. Receivables from and payables to customers include amounts due on cash and margin transactions, including futures contracts transacted on behalf of customers. Securities owned by customers, including those that collateralize margin loans or other similar transactions, are not reported in the condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are expensed 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	'
	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 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 condensed consolidated statements of comprehensive income. The recorded amounts of IBG, Inc.’s equity method investments, $24.7 million at June 30, 2014 ($27.5 million at December 31, 2013), which are reported as a component of other assets in the 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 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, $27.5 million at June 30, 2014 ($27.6 million at December 31, 2013), are recorded at cost or, if an other‑than‑temporary impairment in value has occurred, at a value that reflects management’s estimate of the impairment, and are also components of other assets in the condensed consolidated statements of financial condition. Dividends received from cost basis investments are recognized as a component of other income when 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 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. In general, the practice and intention of the Company is to reinvest the earnings of its non‑U.S. subsidiaries in those operations.
	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.
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. Included in trading gains are net gains and losses on exchange traded options, futures and other derivative instruments. Dividends are integral to the valuation of stocks and interest is integral to the valuation of fixed income instruments. Accordingly, both dividends and interest income and expense attributable to financial instruments owned and financial instruments sold but not yet purchased are reported on a net basis as a component of trading gains in the accompanying 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 condensed consolidated statements of comprehensive income, and the related expenses are reported as execution and clearing expenses.
	—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 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 10) 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.
	IBG, Inc. recognizes interest related to income tax matters as interest income or expense and penalties related to income tax matters as income tax expense.
	Deferred income tax assets and liabilities arise from temporary differences between the tax and financial 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. The Company is not aware of any such changes that would have a material effect on the Company’s results of operations, cash flows, or financial position.
	ASC 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 2014, prior to the issuance of the Company’s condensed consolidated financial statements, ASUs 2014-01 through 2014-14 have been issued. Following is a summary of recently issued ASUs that have affected or may affect the Company’s condensed consolidated financial statements:
			Affects	Status
	ASU 2013-05		Foreign Currency Matters (Topic 830): Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity	Effective for fiscal periods beginning on or after December 15, 2013.
	ASU 2014-06		Technical Corrections and Improvements Related to Glossary Terms	Effective on issuance in March 2014.
	ASU 2014-09		Revenue from Contracts with Customers (Topic 606)	Effective for fiscal periods beginning on or after December 15, 2016.
	ASU 2014-11		Transfers and Servicing (Topic 860): Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures.	Effective for the first interim or annual period beginning after December 15, 2014.
	Adoption of those ASUs that became effective during 2014, prior to the issuance of the Company’s condensed consolidated financial statements, did not have a material effect on those financial statements

Equity_And_Earnings_Per_Share_

Equity And Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2014
Equity And Earnings Per Share [Abstract]	'
Earnings Per Share Basic And Diluted	'
	Earnings per Share
	Basic earnings per share are calculated utilizing net income available for common stockholders divided by the weighted average number of shares of Class A and Class B common stock outstanding for that period:
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Basic earnings per share:
	Net income available for common stockholders	$	15,161	$	10,378	$	34,250	$	16,935
	Weighted average shares of common stock outstanding:
	Class A		56,079,713		48,929,248		55,375,829		48,218,472
	Class B		100		100		100		100
			56,079,813		48,929,348		55,375,929		48,218,572
	Basic earnings per share	$	0.27	$	0.21	$	0.62	$	0.35
	Diluted earnings per share are calculated utilizing the Company’s basic net income available for common stockholders divided by diluted weighted average shares outstanding with no adjustments to net income available to common stockholders for potentially dilutive common shares:
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Diluted earnings per share:
	Net income available for common stockholders	$	15,161	$	10,378	$	34,250	$	16,935
	Weighted average shares of common stock outstanding:
	Class A:
	Issued and outstanding		56,079,713		48,929,248		55,375,829		48,218,472
	Potentially dilutive common shares issuable pursuant to employee incentive plans		1,220,417		83,219		1,298,737		135,526
	Class B		100		100		100		100
			57,300,230		49,012,567		56,674,666		48,354,098
	Diluted earnings per share	$	0.26	$	0.21	$	0.60	$	0.35

Comprehensive_Income_Tables

Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2014
Comprehensive Income Detail [Abstract]	'
Comprehensive Income Table	'
		Three months ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Comprehensive income available for common stockholders, net of tax	$	16,639	$	6,774	$	36,096	$	9,589
	Earnings per share on comprehensive income:
	Basic	$	0.30	$	0.14	$	0.65	$	0.20
	Diluted	$	0.29	$	0.14	$	0.64	$	0.20
	Weighted average common shares outstanding:
	Basic		56,079,813		48,929,348		55,375,929		48,218,572
	Diluted		57,300,230		49,012,567		56,674,666		48,354,098

Financial_Assets_And_Financial1

Financial Assets And Financial Liabilities (Tables)	6 Months Ended
	Jun. 30, 2014
Financial Assets And Financial Liabilities [Abstract]	'
Fair Value Table	'
		Financial Assets At Fair Value as of June 30, 2014
		Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes	$	3,427,880		$	-		$	-		$	3,427,880
	Financial instruments owned:
	Stocks		1,151,367			-			260			1,151,627
	Options		1,072,980			-			-			1,072,980
	Warrants and discount certificates		34,345			-			-			34,345
	U.S. and foreign government securities		16,049			3,866			-			19,915
	Corporate and municipal bonds		91,243			19,920			-			111,163
	Currency forward contracts		-			8,595			-			8,595
	Total financial instruments owned		2,365,984			32,381			260			2,398,625
	Financial instruments owned and pledged as collateral:
	Stocks		759,705			-			-			759,705
	Warrants		273			-			-			273
	U.S. and foreign government securities		78,012			-			-			78,012
	Corporate and municipal bonds		1,477			-			-			1,477
	Total financial instruments owned and pledged as collateral		839,467			-			-			839,467
	Total financial insturments owned		3,205,451			32,381			260			3,238,092
	Other fair value investments, included in other assets:
	Stocks and options		33,159			-			106			33,265
	Corporate and municipal bonds		-			1,696			-			1,696
	Total other fair value investments, included in other assets		33,159			1,696			106			34,961
	Total Financial Assets at Fair Value	$	6,666,490		$	34,077		$	366		$	6,700,933
		Financial Liabilities At Fair Value as of June 30, 2014
		Level 1			Level 2			Level 3			Total
	Financial instruments sold, not yet purchased:
	Stocks	$	1,370,830		$	-		$	77		$	1,370,907
	Options		1,168,783			-			-			1,168,783
	Warrants and discount certificates		603			-			-			603
	U.S. and foreign government securities		1,840			1,049			-			2,889
	Corporate bonds		77,047			10,556			-			87,603
	Currency forward contracts		-			-			-			-
	Total financial instruments sold, not yet purchased		2,619,103			11,605			77			2,630,785
	Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities
	Stocks and options		132,036			-			-			132,036
	Total other fair value liabilities, included in accounts payable, accrued expenses and other liabilities		132,036			-			-			132,036
	Total Financial Liabilities at Fair Value	$	2,751,139		$	11,605		$	77		$	2,762,821
			Financial Assets At Fair Value as of December 31, 2013
			Level 1			Level 2			Level 3			Total
	Securities segregated for regulatory purposes		$	1,300,016		$	-		$	-		$	1,300,016
	Financial instruments owned:
	Stocks			1,243,914			-			57			1,243,971
	Options			1,880,481			-			-			1,880,481
	Warrants and discount certificates			57,144			-			-			57,144
	U.S. and foreign government securities			4,641			2,102			-			6,743
	Corporate and municipal bonds			72,750			18,476			-			91,226
	Currency forward contracts			-			5,748			-			5,748
	Total financial instruments owned			3,258,930			26,326			57			3,285,313
	Financial instruments owned and pledged as collateral:
	Stocks			1,097,734			-			-			1,097,734
	Warrants			233			-			-			233
	U.S. and foreign government securities			64,439			-			-			64,439
	Corporate and municipal bonds			1,125			-			-			1,125
	Total financial instruments owned and pledged as collateral			1,163,531			-			-			1,163,531
	Total financial instruments owned			4,422,461			26,326			57			4,448,844
	Other fair value investments, included in other assets:
	Stocks			25,604			419			101			26,124
	Corporate and municipal bonds			1,776			47,896			-			49,672
	Mortgage backed securities			-			26,892			-			26,892
	Other asset backed securities			-			22,734			-			22,734
	Other			-			5,328			-			5,328
	Total other fair value assets			27,380			103,269			101			130,750
	Total Financial Assets at Fair Value		$	5,749,857		$	129,595		$	158		$	5,879,610
	Financial Liabilities At Fair Value as of December 31, 2013
	Level 1			Level 2			Level 3			Total
Financial instruments sold, not yet purchased:
Stocks	$	1,266,429		$	-		$	3		$	1,266,432
Options		1,793,248			-			-			1,793,248
Warrants and discount certificates		1,215			-			-			1,215
U.S. and foreign government securities		-			4,412			-			4,412
Corporate bonds		77,936			9,628			-			87,564
Currency forward contracts		-			802			-			802
Total financial instruments sold, not yet purchased	$	3,138,828		$	14,842		$	3		$	3,153,673
Level 3 Financial Assets And Financial Liabilities	'
	Balance, January 1, 2014	$	158
	Total gains or losses (realized/unrealized)  - Included in earnings		43
	Purchases, issuances and settlements		-38
	Transfers in and/or out of Level 3		203
	Balance, June 30, 2014	$	366
	Financial liabilities—Level 3 activities:
	Balance, January 1, 2014	$	3
	Total gains or losses (realized/unrealized) - Included in earnings		-
	Purchases, issuances and settlements		-
	Transfers in and/or out of Level 3		74
	Balance, June 30, 2014	$	77
Trading Gains From Market Making Transactions	'
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Equities	$	56,564		$	92,992		$	151,709		$	161,516
	Fixed Income		6,361			6,703			12,091			14,471
	Foreign Exchange		21,095			-40,677			47,732			-98,002
	Commodities		-			88			-			115
	Total Trading Gains	$	84,020		$	59,106		$	211,532		$	78,100
Netting Of Financial Assets And Financial Liabilities	'
		30-Jun-14
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
	Offsetting of Financial Assets:
	Securities segregated for regulatory purposes -purchased under agreements to resell	$	5,913.9	1		$	-		$	5,913.9		$	-5,913.90	$	-	$	-
	Securities borrowed		3,499.2				-			3,499.2			-3,419.00		-		80.2
	Securities purchased under agreements to resell		274.3				-			274.3			-274.3		-		-
	Financial Instruments owned:		-										-
	Options		1,073.0				-			1,073.0			-1,032.50		-		40.5
	Warrants and discount certificates		34.6				-			34.6			-0.6		-		34.0
	Currency forward contracts		8.6				-			8.6			-		-		8.6
	Total	$	10,803.6			$	-		$	10,803.6		$	-10,640.30	$	-	$	163.3
									Net Amounts of			Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
	Offsetting of Financial Liabilities:
	Securities loaned	$	2,932.4			$	-		$	2,932.4		$	-2,932.00	$	-	$	0.4
	Financial instruments sold, not yet purchased:
	Options		1,168.8				-			1,168.8			-1,032.50		-		136.3
	Warrants and discount certificates		0.6				-			0.6			-0.6		-		-
	Currency forward contracts		-				-			-			-		-		-
	Total	$	4,101.8			$	-		$	4,101.8		$	-3,965.10	$	-	$	136.7
		31-Dec-13
						Gross Amounts			Net Amounts of			Gross Amounts Not Offset in the
						Offset in the			Assets Presented			Condensed Consolidated
						Condensed			in the Condensed			Statement
						Consolidated			Consolidated			of Financial Condition
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Assets				Condition			Condition			Instruments		Pledged		Net Amount
	Offsetting of Financial Assets:
	Securities segregated for regulatory purposes - purchased under agreements to resell	$	6,734.2	1		$	-		$	6,734.2		$	-6,734.20	$	-	$	-
	Securities borrowed		2,751.5				-			2,751.5			-2,694.60		-		56.9
	Securities purchased under agreements to resell		386.3				-			386.3			-386.3		-		-
	Financial Instruments owned:
	Options		1,880.5				-			1,880.5			-1,652.80		-		227.7
	Warrants and discount certificates		57.4				-			57.4			-1.2		-		56.2
	Currency forward contracts		5.7				-			5.7			-		-		5.7
	Total	$	11,815.6			$	-		$	11,815.6		$	-11,469.10	$	-	$	346.5
									Net Amounts of				Gross Amounts Not Offset in the
						Gross Amounts			Liabilities			Condensed Consolidated
						Offset in the			Presented in the			Statement
						Condensed			Condensed			of Financial Condition
						Consolidated			Consolidated
		Gross Amounts of				Statement of			Statement of
		Recognized				Financial			Financial			Financial		Cash Collateral
		Liabilities				Condition			Condition			Instruments		Received		Net Amount
	Offsetting of Financial Liabilities:
	Securities loaned	$	2,563.7			$	-		$	2,563.7		$	-2,544.60	$	-	$	19.1
	Financial instruments sold, not yet purchased:
	Options		1,793.2				-			1,793.2			-1,652.80		-		140.4
	Warrants and discount certificates		1.2				-			1.2			-1.2		-		-
	Currency forward contracts		0.8				-			0.8			-		-		0.8
Total	$	4,358.9			$	-		$	4,358.9		$	-4,198.60	$	-	$	160.3
As of June 30, 2014 and December 31, 2013, the Company had $5.91 billion and $6.73 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in “Cash and securities—segregated for regulatory purposes” in the condensed consolidated statements of financial condition

Collateralized_Transactions_Ta

Collateralized Transactions (Tables)	6 Months Ended
	Jun. 30, 2014
Disclosure Collateralized Transactions [Abstract]	'
Amounts Related To Collateralized Transactions	'
			30-Jun-14				31-Dec-13
			Permitted		Sold or		Permitted		Sold or
			to Repledge		Repledged		to Repledge		Repledged
	Securities lending transactions		$	10,023.5	$	3,170.3	$	9,331.9	$	2,504.3
	Agreements to resell 1			6,187.0		6,183.8		7,116.1		7,099.6
	Customer margin assets			14,122.6		5,564.4		11,753.3		4,602.9
			$	30,333.1	$	14,918.5	$	28,201.3	$	14,206.8
		-1		At June 30, 2014, $5.91 billion or 96% (at December 31, 2013, $6.73 billion, or 95%, of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.
Financial Instruments Owned And Pledged Where The Counterparty Has The Right To Repledge	'
			June 30,		December 31,
			2014		2013
	Stocks		$	759.7	$	1,097.8
	Warrants			0.3		0.2
	U.S. and foreign government obligations			78.0		64.4
	Corporate and municipal bonds			1.5		1.1
			$	839.5	$	1,163.5

Employee_Incentive_Plans_Table

Employee Incentive Plans (Tables)	6 Months Ended
	Jun. 30, 2014
Employee Incentive Plans [Abstract]	'
Share Grants And Fair Value	'
			Fair Value at
			Date of Grant
		Shares	($ millions)
	In connection with IPO	927,943	$	27.8
	31-Jul-07	16,665		0.4
	31-Dec-07	1,055,206		32.9
	31-Dec-08	2,065,432		35.6
	31-Dec-09	2,448,031		42.8
	31-Dec-10	2,513,738		43.2
	31-Dec-11	3,411,613		50.8
	6-Jan-12	1,215,866		18.4
	31-Dec-12	3,629,960		50.5
	31-Dec-13	1,894,046		46.2
		19,178,500	$	348.6
2007 Stock Incentive Plan, ROI Summary	'
		Shares
		2007 Stock
		Incentive Plan
	Balance, December 31, 2013	11,647,117
	Granted	-
	Forfeited	-143,185
	Distributed (1)	-2,434,794
	Balance, June 30, 2014	9,069,138
	Shares cumulatively distributed under the 2007 Stock Incentive Plan include 16,238 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)	6 Months Ended
	Jun. 30, 2014
Segment And Geographic Information [Abstract]	'
Segment And Geographic Information	'
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Net revenues:
	Electronic brokerage	$	220.6	$	212.5	$	444.3	$	407.8
	Market making		91.9		67.4		225.0		91.0
	Corporate and eliminations		-3.2		4.0		-5.1		1.2
	Total net revenues	$	309.3	$	283.9	$	664.2	$	500.0
	Income before income taxes:
	Electronic brokerage	$	131.4	$	123.3	$	265.7	$	234.3
	Market making		46.5		7.6		134.6		-21.4
	Corporate and eliminations		-3.7		3.0		-8		3.2
	Total income before income taxes	$	174.2	$	133.9	$	392.3	$	216.1
		June 30,		December 31,
		2014		2013
	Assets:
	Electronic brokerage	$	34,560.6	$	31,333.5
	Market making		12,190.7		12,139.5
	Corporate and eliminations		-6,595.80		-5,602.30
	Total assets	$	40,155.5	$	37,870.7
	The Company operates its automated global business in U.S. and international markets on more than 100 exchanges and market centers. A significant portion of 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 24 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 months ended June 30, 2014 and 2013 (millions):
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	Net revenues:
	United States	$	252.5	$	193.4	$	535.3	$	331.9
	International		60.5		87.4		134.8		167.7
	Corporate and eliminations		-3.7		3.1		-5.9		0.4
	Total net revenues	$	309.3	$	283.9	$	664.2	$	500.0
	Income before income taxes:
	United States	$	165.1	$	99.0	$	362.1	$	151.0
	International		13.1		32.7		38.8		62.6
	Corporate and eliminations		-4		2.2		-8.6		2.5
	Total income before income taxes	$	174.2	$	133.9	$	392.3	$	216.1

Regulatory_Requirements_Tables

Regulatory Requirements (Tables)	6 Months Ended
	Jun. 30, 2014
Regulatory Requirements [Abstract]	'
Summary Of Capital, Capital Requirements And Excess Capital	'
		Net Capital/
		Eligible Equity		Requirement		Excess
	IB LLC	$	2,262.1	$	332.6	$	1,929.5
	TH LLC		436.0		60.3		375.7
	THE		706.8		197.2		509.6
	Other regulated Operating Companies		465.3		47.1		418.2
		$	3,870.2	$	637.2	$	3,233.0

Recovered_Sheet1

Organization and Nature of Business (Details)	6 Months Ended
	Jun. 30, 2014	3-May-07
	segment
Organization And Nature Of Business [Abstract]	'	'
IBG Inc. ownership % of IBG LLC	14.10%	10.00%
Number of operating segments	2	'

Significant_Accounting_Policie2

Significant Accounting Policies (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	3-May-07
Significant Accounting Policies [Abstract]	'	'	'
SIP expense - Year of grant	'	'	50.00%
SIP expense - Remaining vesting period	'	'	50.00%
SIP expense - Employees over 59 in year of grant	'	'	100.00%
Percent of shares forfeited post employment	'	'	50.00%
Over 59 percent of shares eligible	'	'	100.00%
U.S. Treasury Bills	$3,430,000,000	$1,300,000,000	'
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	5,910,000,000	6,730,000,000	'
Equity method investments	24,700,000	27,500,000	'
Cost method investments	$27,500,000	$27,600,000	'
Property and equipment useful lives	'Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years.	'	'

Equity_And_Earnings_Per_Share_1

Equity And Earnings Per Share (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended		36 Months Ended	86 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2014	Jun. 30, 2014	3-May-07
Equity And Earnings Per Share [Line Items]	'	'	'	'	'	'	'	'	'	'
IBG Inc. ownership % of IBG LLC	14.10%	'	14.10%	'	'	'	'	14.10%	14.10%	10.00%
IBG Holdings ownership % of IBG LLC	85.90%	'	85.90%	'	'	'	'	85.90%	85.90%	90.00%
IBG Holdings Redemption of IBG LLC	'	'	'	'	'	'	'	'	'	10.00%
IBG Holdings LLC Ownership Percentage of Class B Common Stock	'	'	'	'	'	'	'	'	'	100.00%
Common stock, par value	$0.01	'	$0.01	'	$0.01	'	'	$0.01	$0.01	'
Preferred stock shares authorized	10,000	'	10,000	'	10,000	'	'	10,000	10,000	'
Preferred stock shares issued	0	'	0	'	0	'	'	0	0	'
Preferred stock shares outstanding	0	'	0	'	0	'	'	0	0	'
Unamortized deferred tax asset arising from equity offerings	$283,500,000	'	$283,500,000	'	$294,700,000	'	'	$283,500,000	$283,500,000	'
Deferred tax asset arising from equity offerings	420,400,000	'	420,400,000	'	'	'	'	420,400,000	420,400,000	'
Percent of Tax Savings Owed to IBG Holdings LLC	'	'	85.00%	'	'	'	'	'	'	'
Percentage of tax savings retained by IBG Inc.	'	'	15.00%	'	'	'	'	'	'	'
Tax savings owed to IBG Holdings LLC	357,400,000	'	357,400,000	'	'	'	'	357,400,000	357,400,000	'
Tax savings retained by IBG Inc.	63,100,000	'	63,100,000	'	'	'	'	63,100,000	63,100,000	'
Tax savings paid to IBG Holdings LLC	'	'	15,700,000	'	'	'	'	'	86,200,000	'
Exchange Agreement Future Redemption Schedule	'	'	'	'	'	'	'	'12.5% annually for seven (7)B years and 2.5% in the eighth year.	'	'
Shares reserved for future issuance	'	'	'	'	'	'	'	'	'	360,000,000
Shares redeemed by IBG Holdings from IBG LLC	'	'	'	'	'	'	5,013,259	'	'	'
Cash Redemptions IBG Holdings	'	'	'	'	'	'	114,000,000	'	'	'
Shares Issued	'	'	'	'	4,683,415	1,983,624	'	'	'	'
Thomas Peterffy and Affiliates Ownership	87.60%	'	87.60%	'	'	'	'	87.60%	87.60%	84.60%
Dividends paid by IBG LLC	'	'	235,800,000	'	'	'	'	'	'	'
Cash dividend paid to IBG, Inc.	'	'	32,300,000	'	'	'	'	'	'	'
Dividends paid to common shareholders	$5,700,000	$5,500,000	$11,176,000	$9,745,000	'	'	'	'	'	'
Declaration Date	'	'	15-Jul-14	'	'	'	'	'	'	'
Dividend per share	$0.10	$0.10	$0.10	'	'	'	'	'	'	'
Payment Date	'	'	12-Sep-14	'	'	'	'	'	'	'
Record Date	'	'	29-Aug-14	'	'	'	'	'	'	'
Common Class A	'	'	'	'	'	'	'	'	'	'
Equity And Earnings Per Share [Line Items]	'	'	'	'	'	'	'	'	'	'
Shares authorized	1,000,000,000	'	1,000,000,000	'	1,000,000,000	'	'	1,000,000,000	1,000,000,000	'
Common stock, shares issued	57,220,459	'	57,220,459	'	54,788,049	'	'	57,220,459	57,220,459	'
Common stock, shares outstanding	57,098,889	'	57,098,889	'	54,664,095	'	'	57,098,889	57,098,889	'
Common Class B	'	'	'	'	'	'	'	'	'	'
Equity And Earnings Per Share [Line Items]	'	'	'	'	'	'	'	'	'	'
Shares authorized	100	'	100	'	100	'	'	100	100	'
Common stock, shares issued	100	'	100	'	100	'	'	100	100	'
Common stock, shares outstanding	100	'	100	'	100	'	'	100	100	'

Equity_And_Earnings_Per_Share_2

Equity And Earnings Per Share (Basic Table) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic earnings per share:	'	'	'	'
Net income available for common stockholders	$15,161	$10,378	$34,250	$16,935
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	56,079,813	48,929,348	55,375,929	48,218,572
Basic earnings per share	$0.27	$0.21	$0.62	$0.35
Common Class A	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	56,079,713	48,929,248	55,375,829	48,218,472
Common Class B	'	'	'	'
Weighted average shares of common stock outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	100	100	100	100

Equity_And_Earnings_Per_Share_3

Equity And Earnings Per Share (Diluted Table) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Diluted earnings per share:	'	'	'	'
Net income available for common stockholders	$15,161	$10,378	$34,250	$16,935
Weighted Average Shares Outstanding [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	56,079,813	48,929,348	55,375,929	48,218,572
Potentially dilutive common shares:	'	'	'	'
Issuable pursuant to 2007 ROI Unit Stock Plan	1,220,417	83,219	1,298,737	135,526
Weighted Average Number of Shares Outstanding, Diluted	57,300,230	49,012,567	56,674,666	48,354,098
Earnings Per Share, Diluted	$0.26	$0.21	$0.60	$0.35
Common Class A	'	'	'	'
Weighted Average Shares Outstanding [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	56,079,713	48,929,248	55,375,829	48,218,472
Common Class B	'	'	'	'
Weighted Average Shares Outstanding [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	100	100	100	100

Comprehensive_Income_Details

Comprehensive Income (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Comprehensive Income Detail [Abstract]	'	'	'	'
Comprehensive income available for common stockholders	$16,639	$6,774	$36,096	$9,589
Earnings per share on comprehensive income:	'	'	'	'
Basic	$0.30	$0.14	$0.65	$0.20
Diluted	$0.29	$0.14	$0.64	$0.20
Weighted average common shares outstanding:	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	56,079,813	48,929,348	55,375,929	48,218,572
Weighted Average Number of Shares Outstanding, Diluted	57,300,230	49,012,567	56,674,666	48,354,098

Financial_Assets_And_Financial2

Financial Assets And Financial Liabilities (Narrative) (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Transfers of financial instruments owned from level 1 to level 2	$700,000	$1,900,000	'
Transfers of financial instruments owned from level 2 to level 1	1,500,000	1,600,000	'
Transfers of financial instruments sold, but not yet purchased from level 1 to level 2	1,400,000	800,000	'
Transfers of financial instruments sold, but not yet purchased from level 2 to level 1	4,500,000	900,000	'
Total financial assets, at fair value	6,700,933,000	'	5,879,610,000
Financial instruments sold but not yet purchased, at fair value	2,630,785,000	'	3,153,673,000
Level 3	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Total financial assets, at fair value	366,000	0	158,000
Financial instruments sold but not yet purchased, at fair value	$77,000	$0	$3,000

Financial_Assets_And_Financial3

Financial Assets And Financial Liabilities (Fair Value Table) (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Securities segregated for regulatory purposes	$3,427,880	$1,300,016	'
Financial instruments owned	2,398,625	3,285,313	'
Financial instruments owned and pledged as collateral	839,467	1,163,531	'
Total financial instruments owned	3,238,092	4,448,844	'
Other fair value investments, included in other assets	34,961	130,750	'
Total Financial Assets at Fair Value	6,700,933	5,879,610	'
Financial instruments sold but not yet purchased, at fair value	2,630,785	3,153,673	'
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	132,036	'	'
Total Financial Liabilities at Fair Value	2,762,821	'	'
Common Stock [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	1,151,627	1,243,971	'
Financial instruments owned and pledged as collateral	759,705	1,097,734	'
Other fair value investments, included in other assets	'	26,124	'
Financial instruments sold but not yet purchased, at fair value	1,370,907	1,266,432	'
Stocks and options [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	33,265	'	'
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	132,036	'	'
Options [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	1,072,980	1,880,481	'
Financial instruments sold but not yet purchased, at fair value	1,168,783	1,793,248	'
Warrants And Discount Certificates [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	34,345	57,144	'
Financial instruments sold but not yet purchased, at fair value	603	1,215	'
Warrants [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned and pledged as collateral	273	233	'
U.S. And Foreign Government Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	19,915	6,743	'
Financial instruments owned and pledged as collateral	78,012	64,439	'
Financial instruments sold but not yet purchased, at fair value	2,889	4,412	'
Corporate And Municipal Bonds [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	111,163	91,226	'
Financial instruments owned and pledged as collateral	1,477	1,125	'
Other fair value investments, included in other assets	1,696	49,672	'
Financial instruments sold but not yet purchased, at fair value	87,603	87,564	'
Mortgage Backed Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	26,892	'
Other Asset Backed Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	22,734	'
Currency Forward Contracts [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	8,595	5,748	'
Financial instruments sold but not yet purchased, at fair value	'	802	'
Other Assets - Investments [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	5,328	'
Level 1	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Securities segregated for regulatory purposes	3,427,880	1,300,016	'
Financial instruments owned	2,365,984	3,258,930	'
Financial instruments owned and pledged as collateral	839,467	1,163,531	'
Total financial instruments owned	3,205,451	4,422,461	'
Other fair value investments, included in other assets	33,159	27,380	'
Total Financial Assets at Fair Value	6,666,490	5,749,857	'
Financial instruments sold but not yet purchased, at fair value	2,619,103	3,138,828	'
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	132,036	'	'
Total Financial Liabilities at Fair Value	2,751,139	'	'
Level 1 | Common Stock [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	1,151,367	1,243,914	'
Financial instruments owned and pledged as collateral	759,705	1,097,734	'
Other fair value investments, included in other assets	'	25,604	'
Financial instruments sold but not yet purchased, at fair value	1,370,830	1,266,429	'
Level 1 | Stocks and options [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	33,159	'	'
Other fair value liabilities, included in accounts payable, accrued expenses and other liabilities	132,036	'	'
Level 1 | Options [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	1,072,980	1,880,481	'
Financial instruments sold but not yet purchased, at fair value	1,168,783	1,793,248	'
Level 1 | Warrants And Discount Certificates [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	34,345	57,144	'
Financial instruments sold but not yet purchased, at fair value	603	1,215	'
Level 1 | Warrants [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned and pledged as collateral	273	233	'
Level 1 | U.S. And Foreign Government Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	16,049	4,641	'
Financial instruments owned and pledged as collateral	78,012	64,439	'
Financial instruments sold but not yet purchased, at fair value	1,840	'	'
Level 1 | Corporate And Municipal Bonds [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	91,243	72,750	'
Financial instruments owned and pledged as collateral	1,477	1,125	'
Other fair value investments, included in other assets	'	1,776	'
Financial instruments sold but not yet purchased, at fair value	77,047	77,936	'
Level 2	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	32,381	26,326	'
Total financial instruments owned	32,381	26,326	'
Other fair value investments, included in other assets	1,696	103,269	'
Total Financial Assets at Fair Value	34,077	129,595	'
Financial instruments sold but not yet purchased, at fair value	11,605	14,842	'
Total Financial Liabilities at Fair Value	11,605	'	'
Level 2 | Common Stock [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	419	'
Level 2 | U.S. And Foreign Government Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	3,866	2,102	'
Financial instruments sold but not yet purchased, at fair value	1,049	4,412	'
Level 2 | Corporate And Municipal Bonds [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	19,920	18,476	'
Other fair value investments, included in other assets	1,696	47,896	'
Financial instruments sold but not yet purchased, at fair value	10,556	9,628	'
Level 2 | Mortgage Backed Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	26,892	'
Level 2 | Other Asset Backed Securities [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	22,734	'
Level 2 | Currency Forward Contracts [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	8,595	5,748	'
Financial instruments sold but not yet purchased, at fair value	'	802	'
Level 2 | Other Assets - Investments [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	'	5,328	'
Level 3	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	260	57	'
Total financial instruments owned	260	57	'
Other fair value investments, included in other assets	106	101	'
Total Financial Assets at Fair Value	366	158	0
Financial instruments sold but not yet purchased, at fair value	77	3	0
Total Financial Liabilities at Fair Value	77	'	'
Level 3 | Common Stock [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Financial instruments owned	260	57	'
Other fair value investments, included in other assets	'	101	'
Financial instruments sold but not yet purchased, at fair value	77	3	'
Level 3 | Stocks and options [Member]	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Other fair value investments, included in other assets	$106	'	'

Financial_Assets_And_Financial4

Financial Assets And Financial Liabilities (Level 3 Financial Assets) (Details) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014
Financial Assets Level 3 Rollforward [Abstract]	'
Beginning balance	$158
Total gains or losses (realized/unrealized) - Included in earnings (Assets)	43
Purchases, issuances and settlements (Assets)	-38
Transfers in and/or out of Level 3 (Assets)	203
Ending balance	$366

Financial_Assets_And_Financial5

Financial Assets And Financial Liabilities (Level 3 Financial Liabilities) (Details) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014
Financial Liabilities Level 3 Rollforward [Abstract]	'
Beginning balance	$3
Transfers in and/or out of Level 3 (Liabilities)	74
Ending balance	$77

Financial_Assets_And_Financial6

Financial Assets And Financial Liabilities (Trading Gains from Market Making Transactions) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Financial Assets And Financial Liabilities [Abstract]	'	'	'	'
Equities	$56,564	$92,992	$151,709	$161,516
Fixed Income	6,361	6,703	12,091	14,471
Foreign Exchange	21,095	-40,677	47,732	-98,002
Commodities	'	88	'	115
Trading gains	$84,020	$59,106	$211,532	$78,100

Financial_Assets_And_Financial7

Financial Assets And Financial Liabilities (Netting of Financial Assets) (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	$10,803.60		$11,815.60
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	10,803.60		11,815.60
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-10,640.30		-11,469.10
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	163.3		346.5
Securities Segregated For Regulatory Purposes - Purchased Under Agreements To Resell [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	5,913.90	[1]	6,734.20	[1]
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	5,913.90		6,734.20
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-5,913.90		-6,734.20
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Securities Borrowed [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	3,499.20		2,751.50
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	3,499.20		2,751.50
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-3,419		-2,694.60
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	80.2		56.9
Securities Purchased Under Agreement to Resell [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	274.3		386.3
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	274.3		386.3
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-274.3		-386.3
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	0		0
Options [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	1,073		1,880.50
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	1,073		1,880.50
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-1,032.50		-1,652.80
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	40.5		227.7
Warrants And Discount Certificates [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	34.6		57.4
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	34.6		57.4
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	-0.6		-1.2
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	34		56.2
Currency Forward Contracts [Member]	'		'
Offsetting Assets [Line Items]	'		'
Gross Amounts of Recognized Assets	8.6		5.7
Gross Amounts Assets Offset in the Consolidated Statement of Financial Condition	0		0
Net Amounts of Assets Presented in the Statement of Financial Condition	8.6		5.7
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Financial Instruments)	0		0
Gross Amounts of Assets Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Received)	0		0
Net Amount of Assets	$8.60		$5.70
[1]	As of June 30, 2014 and December 31, 2013, the Company had $5.91B billion and $6.73B billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in bCash and securitiesbsegregated for regulatory purposesb in the condensed consolidated statements of financial condition

Financial_Assets_And_Financial8

Financial Assets And Financial Liabilities (Netting of Financial Liabilities) (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	$4,101.80	$4,358.90
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	4,101.80	4,358.90
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-3,965.10	-4,198.60
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	136.7	160.3
Securities Loaned [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	2,932.40	2,563.70
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	2,932.40	2,563.70
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-2,932	-2,544.60
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	0.4	19.1
Options Sold, Not Yet Purchased [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	1,168.80	1,793.20
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	1,168.80	1,793.20
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-1,032.50	-1,652.80
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	136.3	140.4
Warrants And Discount Certificates Sold, Not Yet Purchased [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	0.6	1.2
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	0.6	1.2
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	-0.6	-1.2
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	0	0
Currency Forward Contracts Sold, Not Yet Purchased [Member]	'	'
Offsetting Liabilities [Line Items]	'	'
Gross Amounts of Recognized Liabilities	0	0.8
Gross Amounts Liabilities Offset in the Consolidated Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	0	0.8
Gross Amounts of Liabilities Not Offset in the Consolidated Satement of Financial Position (Financial Instruments)	0	0
Gross Amounts Not Offset in the Consolidated Statement of Financial Position (Cash Collateral Pledged)	0	0
Net Amount of Liabilities	$0	$0.80

Collateralized_Transactions_Na

Collateralized Transactions (Narrative) (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Disclosure Collateralized Transactions [Abstract]	'	'
Customer margin loans outstanding	$15,326,943,000	$13,596,650,000
Securities repledged and deposited for customers	$5,910,000,000	$6,730,000,000
Percentage of securities repledged and deposited for customers	96.00%	95.00%

Collateralized_Transactions_Am

Collateralized Transactions (Amounts Related to Collateralized Transactions) (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Permitted To Repledge [Member]	'		'
Collateralized Transactions [Line Items]	'		'
Securities lending transactions	$10,023.50		$9,331.90
Agreements to resell	6,187	[1]	7,116.10	[1]
Customer margin assets	14,122.60		11,753.30
Total collateralized transactions	30,333.10		28,201.30
Sold Or Repledged [Member]	'		'
Collateralized Transactions [Line Items]	'		'
Securities lending transactions	3,170.30		2,504.30
Agreements to resell	6,183.80	[1]	7,099.60	[1]
Customer margin assets	5,564.40		4,602.90
Total collateralized transactions	$14,918.50		$14,206.80
[1]	At June 30, 2014, $5.91 billion or 96% (at December 31, 2013, $6.73 billion, or 95%, of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.

Collateralized_Transactions_Fi

Collateralized Transactions (Financial instruments owned and pledged where the counterparty has the right to repledge) (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Disclosure Collateralized Transactions [Abstract]	'	'
Stocks	$759.70	$1,097.80
Warrants	0.3	0.2
U.S. and foreign government securities	78	64.4
Corporate and municipal bonds	1.5	1.1
Financial Instruments Owned and Pledged as Collateral - Eligible to be Repledged by Counterparty	$839.50	$1,163.50

Senior_Secured_Revolving_Credi1

Senior Secured Revolving Credit Facility (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Senior Secured Revolving Credit Facility [Abstract]	'	'
Senior secured revolving credit facility maximum capacity	$100,000,000	'
Minimum consolidated shareholders' equity	3,600,000,000	'
Quarterly Increases % of Positive Consolidated Net Income	25.00%	'
Maximum debt to capitalization ratio	30.00%	'
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

Employee_Incentive_Plans_Narra

Employee Incentive Plans (Narrative) (Details) (USD $)	0 Months Ended	6 Months Ended			86 Months Ended
In Millions, except Share data, unless otherwise specified	3-May-07	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014	Apr. 24, 2014	Dec. 31, 2013	3-May-07	Dec. 31, 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'		'	'	'	'	'	'
ROI Dollar Unit Payable	'	$3.10		'	$3.10	'	$5.60	'	'
Vested balance of ROI payable	'	3.1		'	3.1	'	5.6	'	'
ROI dollar compensation expense	'	0.3		0.2	'	'	'	'	'
Common Stock Shares issued under ROI Unit Stock Plan	'	'		'	'	'	'	1,271,009	'
ROI Shares issued to IBG LLC	'	'		'	'	'	'	1,250,000	'
2007 SIP shares issued under ROI Unit Stock Plan	'	'		'	'	'	'	21,009	'
Fair value ROI Treasury Stock	'	'		'	'	'	'	38.1	'
Fair Value ROI Accrual	'	'		'	'	'	'	'	17.8
Maximum shares of stock distributable under 2007 Stock Incentive Plan	'	20,000,000		'	20,000,000	30,000,000	20,000,000	'	'
Increase in 2007 Stock Incentive Plan shares	'	'		'	'	10,000,000	'	'	'
Shares granted to external directors	'	'		'	20,423	'	'	'	'
2007 Stock Incentive Plan Compensation Expense	'	21.6		24.1	'	'	'	'	'
Estimated Future 2007 Stock Incentive Plan Compensation Expense	'	$32.50		'	$32.50	'	'	'	'
Percent Shares Forfeited Post Employment	'	'		'	'	'	'	50.00%	'
Over Fifty Nine Percent Unvested Shares Eligible	'	'		'	'	'	'	100.00%	'
Former employees vesting schedule (Years)	'5 years	'		'	'	'	'	'	'
Post employment vesting percentage (Years 1 - 4)	'	'		'	'	'	'	12.50%	'
Post employment vesting percentage (Year 5)	'	'		'	'	'	'	50.00%	'
Post employment shares distribution	'	'		'	173,457	'	'	'	'
Incentive Plan Shares Distributed From Treasury [Member]	'	'		'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'		'	'	'	'	'	'
Shares Distributed	'	'		'	16,238	'	'	'	'
2007 ROI Unit Stock Plan [Member]	'	'		'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'		'	'	'	'	'	'
Vesting Percentage	'	'b" 10% on the date of the IPO (or on the first anniversary of the IPO, in the case of U.S. ROI Unit holders who made the above-referenced elections after DecemberB 31, 2006); andb" an additional 15% on each of the first six anniversaries of the date of the IPO, assuming continued employment with IBG,B Inc. and compliance with other applicable covenants.		'	'	'	'	'	'
2007 Stock Incentive Plan (Shares)	'	'		'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'		'	'	'	'	'	'
Vesting Percentage	'	'b" 10% on the first vesting date, which approximates the anniversary of the IPO; andb" an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with IBG,B Inc. and compliance with non-competition and other applicable covenants.		'	'	'	'	'	'
Shares Distributed	'	-2,434,794	[1]	'	'	'	'	'	'
[1]	Shares cumulatively distributed under the 2007 Stock Incentive Plan include 16,238 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.

Employee_Incentive_Plans_Share

Employee Incentive Plans (Share Grants And Fair Value) (Details) (USD $)	86 Months Ended
In Millions, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 06, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Jul. 31, 2007	3-May-07
Employee Incentive Plans [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Shares granted	'	1,894,046	3,629,960	1,215,866	3,411,613	2,513,738	2,448,031	2,065,432	1,055,206	16,665	927,943
Fair Value - Date of Grant ($000's)	'	$46.20	$50.50	$18.40	$50.80	$43.20	$42.80	$35.60	$32.90	$0.40	$27.80
Shares Granted IPO to Date	19,178,500	'	'	'	'	'	'	'	'	'	'
Fair Value - Date of Grant ($000's) IPO to Date	$348.60	'	'	'	'	'	'	'	'	'	'

Employee_Incentive_Plans_2007_

Employee Incentive Plans (2007 Stock Incentive Plan, ROI Summary) (Details) (2007 Stock Incentive Plan (Shares))	6 Months Ended
	Jun. 30, 2014
2007 Stock Incentive Plan (Shares)	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Beginning Balance	11,647,117
Shares Granted	'
Shares Forfeited	-143,185
Shares Distributed	-2,434,794	[1]
Ending Balance	9,069,138
[1]	Shares cumulatively distributed under the 2007 Stock Incentive Plan include 16,238 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.

Income_Taxes_Details

Income Taxes (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Income Taxes [Abstract]	'	'
Undistributed accumulated earnings of foreign subsidiaries	$1,082.90	$1,072.90
Accumulated earnings of foreign pass through subsidiaries	405.6	422.3
Accumulated earnings subject to additional foreign tax	$303.70	$318.70

Recovered_Sheet2

Commitments, Contingencies and Guarantees (Details) (USD $)	1 Months Ended	9 Months Ended	6 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Jun. 30, 2014	Jun. 30, 2014
			Scenario, Forecast [Member]
Commitment And Contingencies [Line Items]	'	'	'
Percentage of loss on securities	90.00%	'	'
Loss on large positions on Singapore Exchange	$64	$79.20	$84

Segment_And_Geographic_Informa2

Segment And Geographic Information (Segment Table) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	$309,299	$283,956	$664,207	$500,030	'
Income before income taxes	174,209	133,926	392,353	216,149	'
Assets	40,155,499	'	40,155,499	'	37,870,700
Electronic Brokerage [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	220,600	212,500	444,300	407,800	'
Income before income taxes	131,400	123,300	265,700	234,300	'
Assets	34,560,600	'	34,560,600	'	31,333,500
Market Making [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	91,900	67,400	225,000	91,000	'
Income before income taxes	46,500	7,600	134,600	-21,400	'
Assets	12,190,700	'	12,190,700	'	12,139,500
Corporate And Eliminations [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Net revenues	-3,200	4,000	-5,100	1,200	'
Income before income taxes	-3,700	3,000	-8,000	3,200	'
Assets	($6,595,800)	'	($6,595,800)	'	($5,602,300)

Segment_And_Geographic_Informa3

Segment And Geographic Information (Geographic Table) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	$309,299	$283,956	$664,207	$500,030
Income before income taxes	174,209	133,926	392,353	216,149
United States [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	252,500	193,400	535,300	331,900
Income before income taxes	165,100	99,000	362,100	151,000
International [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	60,500	87,400	134,800	167,700
Income before income taxes	13,100	32,700	38,800	62,600
Corporate And Eliminations [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Net revenues	-3,700	3,100	-5,900	400
Income before income taxes	($4,000)	$2,200	($8,600)	$2,500

Regulatory_Requirements_Narrat

Regulatory Requirements (Narrative) (Details) (USD $)	Jun. 30, 2014
In Millions, unless otherwise specified
Regulatory Requirements [Abstract]	'
Excess regulatory capital	$3,233

Regulatory_Requirements_Summar

Regulatory Requirements (Summary Of Capital, Capital Requirements And Excess Capital) (Details) (USD $)	Jun. 30, 2014
In Millions, unless otherwise specified
Net Capital / Eligible Equity	$3,870.20
Required net capital	637.2
Excess regulatory capital	3,233
IB LLC [Member]	'
Net Capital / Eligible Equity	2,262.10
Required net capital	332.6
Excess regulatory capital	1,929.50
TH LLC [Member]	'
Net Capital / Eligible Equity	436
Required net capital	60.3
Excess regulatory capital	375.7
THE [Member]	'
Net Capital / Eligible Equity	706.8
Required net capital	197.2
Excess regulatory capital	509.6
Other Regulated Operating Companies [Member]	'
Net Capital / Eligible Equity	465.3
Required net capital	47.1
Excess regulatory capital	$418.20

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Related Party Transactions [Abstract]	'	'
Due from Related Parties - Customers	$1.80	$0.40
Due to Related Parties - Customers	$409.80	$815.50