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Organization and Basis of Presentation (Details)	Sep. 30, 2011
Organization and Basis of Presentation
Threshold percentage for goodwill impairment testing	50.00%

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- Definition

Represents the threshold percentage of likelihood of fair value of reporting unit being less than carrying amount to be considered for goodwill impairment testing.

+ Details

Name:	itg_ThresholdPercentageForGoodwillImpairmentTesting
Namespace Prefix:	itg
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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- Details

Name:	us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration