| Label                                            | **Element**              | Value                                                                                                                                                                                                                                                    |
|--------------------------------------------------|--------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Risk/Return:**                                 | rr_RiskReturnAbstract    |                                                                                                                                                                                                                                                     |
| Registrant Name                                  | dei_EntityRegistrantName | FIDELITY INVESTMENT TRUST                                                                                                                                                                                                                                |
| Prospectus Date                                  | rr_ProspectusDate        | Dec. 30,  2014                                                                                                                                                                                                                                           |
| A T C | Fidelity Emerging Markets Discovery Fund |                          |                                                                                                                                                                                                                                                     |
| **Risk/Return:**                                 | rr_RiskReturnAbstract    |                                                                                                                                                                                                                                                     |
| Supplement [Text Block]                          | fit_SupplementTextBlock  | **Supplement to the Fidelity Advisor® Emerging Markets Discovery Fund Class A, Class T, and Class C December 30, 2014 Prospectus**Effective October 1, 2015, the fund changed its classification from a non-diversified fund to a diversified fund. |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1
+ Details**Name:**dei_EntityRegistrantName**Namespace Prefix:**dei_**Data Type:**xbrli:normalizedStringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Supplement Text Block.
+ References
No definition available.
+ Details**Name:**fit_SupplementTextBlock**Namespace Prefix:**fit_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The date of the prospectus.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 1 -Subsection a -Paragraph 3
+ Details**Name:**rr_ProspectusDate**Namespace Prefix:**rr_**Data Type:**xbrli:dateItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
+ Details**Name:**rr_RiskReturnAbstract**Namespace Prefix:**rr_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_DocumentInformationDocumentAxis=fit_ClassAtcMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=fit_S000034264Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |