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Acquisitions - Narrative (Details) | 3 Months Ended
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Mar. 31, 2018 acquisition
Acquisitions 2018 |
Acquisitions |
Number of businesses acquired | 1

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- References No definition available. + Details
Name: | us-gaap_BusinessCombinationConsiderationTransferredAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of businesses acquired by the entity during the period. + References No definition available. + Details
Name: | us-gaap_NumberOfBusinessesAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=int_Acquisitions2018Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |