Receivables and Payables - Securities Borrowed and Loaned (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2016
Securities Borrowed and Loaned
Interest earned	$ 448	$ 2,080
Interest incurred	(185)	(1,251)
Interest earned (incurred), net	$ 263	$ 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