Receivables and Payables - Securities Borrowed and Loaned (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Securities Borrowed and Loaned
Interest earned	$ 1,961	$ 5,512
Interest incurred	(1,132)	(3,720)
Interest earned (incurred), net	$ 829	$ 1,792

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