Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Feb. 19, 2014	Jun. 30, 2013
Document and Entity Information
Entity Registrant Name	INVESTMENT TECHNOLOGY GROUP, INC.
Entity Central Index Key	0000920424
Document Type	10-K/A
Document Period End Date	Dec. 31, 2013
Amendment Flag	true
Amendment Description	Investment Technology Group, Inc. (the "Company") is filing this Amendment No. 1 on Form 10-K/A (this "Amendment") to its Annual Report on Form 10-K for the year ended December 31, 2013 filed with the U.S. Securities and Exchange Commission ("SEC") on March 17, 2014 (the "Original Filing") solely to (a) include a reference to the XBRL Taxonomy Extension Definition Linkbase Document in the Exhibit List in Item 15 that was inadvertently omitted in the Original Filing and (b) to correct typographical errors, as follows: (i) Item 8: Amend (a) the Report of Independent Registered Public Accounting Firm relating to the consolidated financial statements on page 50 of the Original Filing (the "KPMG Financial Statement Report") to reflect the correct date of the referenced Report of Independent Registered Public Accounting Firm relating to the effectiveness of the Company’s internal control over financial reporting (the "KPMG Internal Control Report"), which was the date of the Original Filing, March 17, 2014 and (b) the net amount for deposits received for securities loaned as of December 31, 2013 on page 74 of the Original Filing to "(15,968)" from "(15,698)"; (ii) Item 9A: Amend the KPMG Internal Control Report on page 99 of the Original Filing to reflect the correct date of the referenced KPMG Financial Statement Report, which was the date of the Original Filing, March 17, 2014; and (iii) Item 15: Amend Exhibit 23.1 (Consent of Independent Registered Public Accounting Firm) to reflect the correct date of the referenced KPMG Financial Statement Report and KPMG Internal Control Report, which, in each case, was the date of the Original Filing, March 17, 2014. This Amendment also hereby amends the date of the signature of the Chief Financial Officer on behalf of the Company on page 105 of the Original Filing, which was the date of the Original Filing, March 17, 2014. Although Items 8, 9A and 15 are restated in their entirety, this Amendment does not amend or otherwise update any information in the Original Filing, except as set forth above. Specifically, no information in the Company’s financial statements was altered or restated. Accordingly, this Amendment should be read in conjunction with the Original Filing and with our filings with the SEC subsequent to the Original Filing, if any.
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 506,073,889
Entity Common Stock, Shares Outstanding		35,839,452
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	FY