Receivables and Payables - Customers (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Receivables from customers
Customers	$ 75,062	$ 55,006
Allowance for doubtful accounts	(367)	(520)
Total	74,695	54,486
Payables to customers
Customers	23,568	12,272
Total	$ 23,568	$ 12,272

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

Name:	itg_ReceivablesFromCustomersAbstract
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- Definition

Represents the allowance for doubtful accounts on receivables from customers.

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No definition available.

+ Details

Name:	itg_ReceivablesFromCustomersAllowanceForDoubtfulAccounts
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- Definition

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

+ References

No definition available.

+ Details

Name:	itg_ReceivablesFromCustomersGross
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Data Type:	xbrli:monetaryItemType
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

+ Details

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- Definition

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

+ References

+ Details

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