Net Capital Requirement (Details) (USD $)	Mar. 31, 2013
Canadian Operations
Net Capital Requirement
Net Capital	$ 37,900,000
Excess Net Capital	37,400,000
European Operations
Net Capital Requirement
Net Capital	50,500,000
Excess Net Capital	17,600,000
Australia
Net Capital Requirement
Net Capital	13,900,000
Excess Net Capital	4,500,000
Hong Kong
Net Capital Requirement
Net Capital	27,700,000
Excess Net Capital	7,000,000
Singapore
Net Capital Requirement
Net Capital	400,000
Excess Net Capital	200,000
ITG Inc.
Net Capital Requirement
Minimum net capital under the alternative method	1,000,000
Net capital percentage of debit balances arising from customer transactions	2.00%
Net capital percentage of aggregate indebtedness	6.66%
Minimum net capital under the basic method	1,000,000
Cash balance in a Special Reserve Bank Account for the benefit of customers and brokers under the Customer Protection Rule	5,900,000
ITG Inc. | U.S. Operations
Net Capital Requirement
Net Capital	97,400,000
Excess Net Capital	95,100,000
Alter Net
Net Capital Requirement
Net capital percentage of aggregate indebtedness	6.66%
Minimum net capital under the basic method	100,000
Alter Net | U.S. Operations
Net Capital Requirement
Net Capital	4,900,000
Excess Net Capital	4,700,000
ITG Derivatives | U.S. Operations
Net Capital Requirement
Net Capital	4,200,000
Excess Net Capital	$ 3,200,000