Receivables and Payables (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Receivables from brokers, dealers and clearing organizations
Broker-dealers	$ 190,338,000us-gaap_DueFromCorrespondentBrokers		$ 147,240,000us-gaap_DueFromCorrespondentBrokers
Clearing organizations	1,944,000		1,447,000
Securities borrowed	690,345,000		496,596,000
Allowance for doubtful accounts	(740,000)		(669,000)
Total	881,887,000		644,614,000
Payables to brokers, dealers and clearing organizations
Broker-dealers	47,623,000us-gaap_DueToCorrespondentBrokers		51,615,000us-gaap_DueToCorrespondentBrokers
Clearing organizations	3,400,000itg_PayablesToClearingOrganizations		39,433,000itg_PayablesToClearingOrganizations
Securities loaned	737,941,000		508,993,000
Total	788,964,000		600,041,000
Receivables from customers
Customers	110,932,000itg_ReceivablesFromCustomersGross		108,518,000itg_ReceivablesFromCustomersGross
Allowance for doubtful accounts	(707,000)		(583,000)
Total	110,225,000us-gaap_ReceivablesFromCustomers		107,935,000us-gaap_ReceivablesFromCustomers
Payables to customers
Customers	29,775,000itg_PayablesToCustomersGross		11,132,000itg_PayablesToCustomersGross
Total	29,775,000us-gaap_PayablesToCustomers		11,132,000us-gaap_PayablesToCustomers
Securities Borrowed and Loaned
Fair value of securities borrowed	692,000,000
Interest earned	1,408,000itg_InterestIncomeOnSecuritiesBorrowed	4,403,000itg_InterestIncomeOnSecuritiesBorrowed
Interest incurred	(1,046,000)itg_InterestExpenseSecuritiesLoaned	(3,066,000)itg_InterestExpenseSecuritiesLoaned
Interest earned (incurred), net	362,000	1,337,000
Deposits paid for securities borrowed
Gross Amounts of Recognized Assets	690,345,000us-gaap_SecuritiesBorrowedGross		496,596,000us-gaap_SecuritiesBorrowedGross
Net Amounts Presented in the Consolidated Statement of Financial Condition	690,345,000us-gaap_SecuritiesBorrowed		496,596,000us-gaap_SecuritiesBorrowed
Collateral Received or Pledged (including Cash)	690,345,000		496,374,000
Net Amount			222,000
Deposits received for securities loaned
Gross Amounts of Recognized Liabilities	(737,941,000)us-gaap_SecuritiesLoanedGross		(508,993,000)us-gaap_SecuritiesLoanedGross
Net Amounts Presented in the Consolidated Statement of Financial Condition	(737,941,000)us-gaap_SecuritiesLoaned		(508,993,000)us-gaap_SecuritiesLoaned
Collateral Received or Pledged (including Cash)	(718,439,000)		(497,462,000)
Net Amount	$ (19,502,000)		$ (11,531,000)

The gross amounts of interest incurred on cash received from counterparties as collateral for securities loaned.

No definition available.

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The net amount of interest earned and incurred on securities borrowed and securities loaned transactions.

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The gross amount of interest earned on cash provided to counterparties as collateral for securities borrowed.

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Amounts payable to clearing organizations on open transactions and floor-brokerage payables.

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Gross amount due to customers for fees and charges arising from transactions related to the entity's brokerage activities and operations.

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Represents the allowance for doubtful accounts on receivables from brokers, dealers and clearing organizations.

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Represents the allowance for doubtful accounts on receivables from customers.

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Gross amount due from customers for fees and charges arising from transactions related to the entity's brokerage activities and operations.

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This is the amount of cash advanced as security in return for borrowing securities from another party.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

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The amount of cash received as security in return for loaning securities to another party.

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-Name Regulation S-X (SX)

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Amount receivable from correspondent broker-dealer.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

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Amount payable to correspondent broker-dealer.

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Amount payable to broker-dealers and clearing organizations, including, but not limited to, securities failed-to-receive, certain deposits received for securities loaned, open transactions, and floor-brokerage payables.

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Amounts payable to customers at the balance sheet date. The term customers generally excludes other broker-dealers; persons who are principal officers, directors, and stockholders; and persons whose securities or funds are part of the regulatory net capital of the broker-dealer. Another broker-dealer's account can be classified as a customer if the account is carried as an omnibus account in compliance with certain regulations. The accounts of principal officers, directors and stockholders may be combined in the customer captions if they are not material and the combination is disclosed in the oath that is required to accompany the annual audited FOCUS Report.

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-Number 240

-Section 1

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Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables.

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Amount of right to receive cash and securities on deposit with clearing organizations. Clearing organizations perform post trade processing and trade comparisons among numerous broker-dealers and act as settlement agents between buying and selling broker-dealers.

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Amount due from customers for fees and charges arising from transactions related to the entity's brokerage activities and operations.

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Amount, after the effects of master netting arrangements, of securities borrowed from entities in exchange for collateral. Includes assets not subject to a master netting arrangement.

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Amount of securities borrowed from entities in exchange for collateral offset against an obligation to return collateral under a master netting arrangement. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of obligation to return securities collateral under master netting arrangements that have not been offset against securities borrowed.

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Fair value portion of securities borrowed from other entities.

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No definition available.

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Amount, before effects of master netting arrangements, of securities borrowed from entities in exchange for collateral.

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Amount, after the effects of master netting arrangements, of securities loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement.

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Amount of securities loaned to entities in exchange for collateral offset against a right to receive collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of right to receive securities collateral under master netting arrangements that have not been offset against securities loaned.

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Amount, before effects of master netting arrangements, of securities loaned to entities in exchange for collateral.

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