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Basis of Presentation and Nature of Operations - Additional Information (Details) - Minimum	Dec. 31, 2020 Office
Domestic
Basis of Presentation and Nature of Operations [Line Items]
Number of offices	56
International
Basis of Presentation and Nature of Operations [Line Items]
Number of offices	22

X

- Definition

Basis of presentation and nature of operations.

+ References

No definition available.

+ Details

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X

- Definition

The number of offices owned by the company.

+ References

No definition available.

+ Details

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Namespace Prefix:	icfi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Details

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Namespace Prefix:
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X

- Details

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X

- Details

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Namespace Prefix:
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