Acquisitions and Significant Accounting Policies (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Accounts Receivable Purchase Agreement
Maximum amount of accounts receivable to be sold under a Receivables Purchase Agreement ("RPA")	$ 100.0		$ 100.0
Percentage of the sold accounts receivable the sales price is equal to before a discount margin, high end of range	100.00%		100.00%
Percentage of the sold accounts receivable the sales price is equal to before a discount margin, low end of range	90.00%		90.00%
Percentage rate added to floating market rate to get discount margin subtracted from sold accounts receivable balance	2.00%		2.00%
Percentage of retained beneficial interest in accounts receivable sold	10.00%		10.00%
Accounts receivable sold	41.8		41.8
Retained beneficial interest recorded			4.1
Goodwill
Increase in goodwill due to acquisitions			56.9
Change in goodwill due to foreign currency translation adjustments			(0.8)
Extinguishment of Liability
Derecognized vendor liability accruals amount	$ 2.7	$ 3.3	$ 5.9	$ 7.9

Name:	int_AccountsReceivablePurchaseAgreementAbstract
Namespace Prefix:	int
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the amount of accounts receivable sold at the end of the period.

+ Details

Name:	int_AccountsReceivableSoldAmount
Namespace Prefix:	int
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the derecognized vendor liability accruals amount due to the legal release of the entity's obligations.

+ Details

Name:	int_DerecognizedVendorLiabilityAccrualsAmount
Namespace Prefix:	int
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	int_ExtinguishmentOfLiabilityAbstract
Namespace Prefix:	int
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	int_GoodwillAbstract
Namespace Prefix:	int
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of retained beneficial interest in the accounts receivable sold.

+ Details

Name:	int_PercentageOfRetainedBeneficialInterestInAccountsReceivableSold
Namespace Prefix:	int
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the higher end of percentage of the sold accounts receivable the sales price is equal to before a discount margin.

+ Details

Name:	int_PercentageOfSoldAccountsReceivableSalePriceEqualToBeforeDiscountMarginHighEndOfRange
Namespace Prefix:	int
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the lower end of percentage of the sold accounts receivable the sales price is equal to before a discount margin.

+ Details

Name:	int_PercentageOfSoldAccountsReceivableSalePriceEqualToBeforeDiscountMarginLowEndOfRange
Namespace Prefix:	int
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage rate added to floating market rate to get discount margin subtracted from sold accounts receivable balance.

+ Details

Name:	int_PercentageRateAddedToFloatingMarketRateToGetDiscountMargin
Namespace Prefix:	int
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the amount of retained beneficial interest recorded during the period.

+ Details

Name:	int_RetainedBeneficialInterestAmount
Namespace Prefix:	int
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate amount of goodwill acquired in the period and allocated to the reportable segment. The value is stated at fair value based on the purchase price allocation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6905597&loc=d3e13816-109267

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 72

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph e

-Clause 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

The increase (decrease) to the recorded value of goodwill for foreign currency translation adjustments.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Subparagraph e

-Paragraph 45

-Clause 6

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The face amount of all receivables that will be sold to other entities, including trade and loan receivables.

+ References

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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=6375948&loc=d3e4428-111522

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant