Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 23, 2015
Entity Registrant Name	ICF International, Inc.
Entity Central Index Key	0001362004
Trading Symbol	icfi
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		19,223,827
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Amendment Flag	false