Receivables and Payables - Securities Borrowed and Loaned (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Securities Borrowed and Loaned
Interest earned	$ 1,961
Interest incurred	(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