Net Capital Requirement (Details) (USD $)	Sep. 30, 2013
Canadian Operations
Net Capital Requirement
Net Capital	$ 43,600,000
Excess Net Capital	43,100,000
European Operations
Net Capital Requirement
Net Capital	56,200,000
Excess Net Capital	24,700,000
Australia
Net Capital Requirement
Net Capital	12,200,000
Excess Net Capital	6,100,000
Hong Kong
Net Capital Requirement
Net Capital	29,400,000
Excess Net Capital	15,800,000
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 under the Customer Protection Rule	10,600,000
Cash balance under PAIB agreements	400,000
ITG Inc. | U.S. Operations
Net Capital Requirement
Net Capital	102,200,000
Excess Net Capital	101,200,000
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	5,300,000
Excess Net Capital	5,100,000
ITG Derivatives | U.S. Operations
Net Capital Requirement
Net Capital	4,700,000
Excess Net Capital	$ 3,700,000