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Regulatory Requirements Table (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
All Operating Companies
Excess regulatory capital	$ 2,455.5
Net Capital / Eligible Equity	2,978.6
Required net capital	523.1
IB LLC
Excess regulatory capital	1,429.2
Net Capital / Eligible Equity	1,685.9
Required net capital	256.7
TH LLC
Excess regulatory capital	239.0
Net Capital / Eligible Equity	290.3
Required net capital	51.3
THE
Excess regulatory capital	433.8
Net Capital / Eligible Equity	623.5
Required net capital	189.7
Other regulated operating companies
Excess regulatory capital	353.5
Net Capital / Eligible Equity	378.9
Required net capital	$ 25.4

X

- Definition

Eligible equity is equal to the sum of audited capital and reserves and the eligible portion of subordinated debt. Net capital is equal to the net worth of the broker dealer, less certain items such as exchange memberships, carrying value of securities not readily marketable, haircuts on marketable securities in proprietary accounts, furniture and equipment and other illiquid assets as defined.

+ References

No definition available.

+ Details

Name:	ibkr_NetCapitalEligibleEquity
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The amount by which the company's Total Capital exceeds the minimum required for capital adequacy purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 15

-Subparagraph 3a

-IssueDate 2006-05-01

-Chapter 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_ExcessCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The minimum amount of net capital required to be maintained by the entity to engage in securities transactions.

+ References

No definition available.

+ Details

Name:	us-gaap_MinimumNetCapitalRequiredForEntity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant