Receivables and Payables - Securities Borrowed and Loaned (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2016
Securities Borrowed and Loaned
Interest earned	$ 3	$ 1,961
Interest incurred	$ (3)	(1,132)
Interest earned (incurred), net		$ 829

The net amount of interest earned and incurred on securities borrowed and securities loaned transactions.

No definition available.

Name:	itg_InterestIncomeExpenseNetOnSecuritiesBorrowedAndLoaned
Namespace Prefix:	itg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration