Change in contract with customer assets liability net current.

No definition available.

Name:	icfi_ChangeInContractWithCustomerAssetsLiabilitiesNetCurrent
Namespace Prefix:	icfi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Revenue from contract with customer.

+ References

No definition available.

+ Details

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

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130549-203045

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

+ Details

Name:	us-gaap_IncreaseDecreaseInDeferredRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=icfi_USFederalGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=icfi_HealthEducationAndSocialProgramsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=icfi_EnergyEnvironmentalAndInfrastructureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=icfi_SafetyAndSecurityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=icfi_USStateAndLocalGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=icfi_InternationalGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=icfi_CommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=icfi_ConsumerAndFinancialServicesMember
Namespace Prefix:
Data Type:	na
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Revenue Recognition - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Revenue From Contract With Customer [Line Items]
Net contract assets (liabilities)	$ 59,454
Revenue related to contract liabilities	20,900	$ 15,100
U.S. Federal Government \| Health, Education and Social Programs
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	39,400
U.S. Federal Government \| Energy, Environmental and Infrastructure
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	6,200
U.S. Federal Government \| Safety and Security
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	(1,200)
U.S. State and Local Government \| Health, Education and Social Programs
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	7,400
U.S. State and Local Government \| Energy, Environmental and Infrastructure
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	500
International Government \| Health, Education and Social Programs
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	1,700
International Government \| Energy, Environmental and Infrastructure
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	(11,100)
International Government \| Safety and Security
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	(600)
Commercial \| Health, Education and Social Programs
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	(1,200)
Commercial \| Energy, Environmental and Infrastructure
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	(2,600)
Commercial \| Consumer And Financial Services
Revenue From Contract With Customer [Line Items]
Increase (decrease) in revenue	$ (3,500)