Net Capital Requirement (Details) (USD $)	Sep. 30, 2014
Canadian Operations
Net Capital Requirement
Net Capital	$ 40,364,000
Excess Net Capital	39,916,000
Ireland
Net Capital Requirement
Net Capital	72,948,000
Excess Net Capital	21,802,000
U.K.
Net Capital Requirement
Net Capital	4,060,000
Excess Net Capital	3,140,000
Australia
Net Capital Requirement
Net Capital	18,931,000
Excess Net Capital	7,946,000
Hong Kong
Net Capital Requirement
Net Capital	28,037,000
Excess Net Capital	12,243,000
Singapore
Net Capital Requirement
Net Capital	367,000
Excess Net Capital	171,000
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%
Cash balance in a Special Reserve Bank Account for the benefit of customers under the Customer Protection Rule	10,700,000
Cash balance under Proprietary Accounts for Introducing Brokers agreements	400,000
ITG Inc. | U.S. Operations
Net Capital Requirement
Net Capital	73,147,000
Excess Net Capital	73,147,000
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	4,817,000
Excess Net Capital	4,597,000
ITG Derivatives
Net Capital Requirement
Minimum net capital under the basic method	1,000,000
ITG Derivatives | U.S. Operations
Net Capital Requirement
Net Capital	4,626,000
Excess Net Capital	$ 3,626,000