Cash Restricted or Segregated Under Regulations and Other (Details)	12 Months Ended
Dec. 31, 2011 Lease	Dec. 31, 2010 Lease
Cash Restricted or Segregated Under Regulations and Other
Number of MacGregor leases supported by a bank guarantee	2	2

Represents the number of leases supported by a bank guarantee.

No definition available.

Name:	itg_NumberOfLeasesSupportedByBankGuarantee
Namespace Prefix:	itg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration