Increase in borrowings during the period under the debt agreement.

No definition available.

Name:	int_DebtInstrumentIncreaseInBorrowings
Namespace Prefix:	int_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum additional borrowing capacity available under the credit facility at the entity's request subject to satisfaction of certain conditions.

+ References

No definition available.

+ Details

Name:	int_LineOfCreditFacilityMaximumAdditionalBorrowingCapacity
Namespace Prefix:	int_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtLongtermAndShorttermCombinedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentAxis=int_LettersOfCreditAndBankersAcceptanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=int_OtherUncommittedCreditLinesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Jan. 30, 2015	Jan. 29, 2015	Dec. 31, 2013
Credit facility
Debt
Maximum borrowing capacity		$ 1,260.0	$ 1,100.0
Amount outstanding	420.0			200.0
Maximum additional borrowings available at the entity's request subject to satisfaction of certain conditions	150.0
Unused portion of facility	665.2			892.6
Commitment fee on the unused portion of the credit facility (as a percent)	0.30%
Credit facility \| Base rate
Debt
Basis points added to reference rate (as a percent)	1.25%
Credit facility \| Eurodollar rate
Debt
Basis points added to reference rate (as a percent)	2.25%
Letters of credit and bankers' acceptances
Debt
Maximum borrowing capacity	400.0
Letters of credit fees (as a percent)	2.50%
Letters of credit, outstanding amount	14.8			7.4
Term Loans
Debt
Increase in borrowings		100.0
Amount outstanding	241.3	341.3		242.5
Term Loans \| Base rate
Debt
Basis points added to reference rate (as a percent)	1.25%
Term Loans \| Eurodollar rate
Debt
Basis points added to reference rate (as a percent)	2.25%
Other uncommitted credit lines
Debt
Letters of credit, outstanding amount	$ 211.4			$ 150.6