XML 64 R49.htm IDEA: XBRL DOCUMENT
v3.20.4

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
Name: | icfi_BasisOfPresentationAndNatureOfOperationsLineItems
Namespace Prefix: | icfi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of offices owned by the company. + References No definition available. + Details
Name: | icfi_NumberOfOffices
Namespace Prefix: | icfi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=us-gaap_NonUsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |