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Commitments and Contingencies - Deferred Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
U.S. defined contribution plan
Deferred Compensation Plans
Employer match for each 1% of the participants contributions up to 6% of the participants contributions (as a percent)	50.00%
Percentage of eligible compensation up to 6% of the eligible compensation, matched 50% by employer	1.00%
Employer contribution limit per calendar year (as a percent of compensation)	6.00%
NQDC plan | Other long-term liabilities
Deferred Compensation Plans
Deferred compensation payable	$ 3.3	$ 2.3

X

- Definition

The limit of annual employer contributions to the plan per calendar year as a percentage of compensation.

+ References

No definition available.

+ Details

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Namespace Prefix:	int_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the employer matching contributions for the employees' contributions.

+ References

No definition available.

+ Details

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Namespace Prefix:	int_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the first level of employee contributions (percentage of compensation) which are matched by the employer.

+ References

No definition available.

+ Details

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Namespace Prefix:	int_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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

X

- Details

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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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X

- Details

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