Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 28, 2017
Document Information [Line Items]
Entity Registrant Name	ICF International, Inc.
Entity Central Index Key	0001362004
Trading Symbol	icfi
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		18,799,705
Document Type	10-Q/A
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Amendment Flag	true
Amendment Description	The sole purpose of this Amendment No. 1 on Form 10-Q/A to ICF International, Inc.'s Quarterly Report on Form 10-Q for the quarter ended March 31, 2017, filed with the Securities and Exchange Commission on May 4, 2017 (the "Form 10-Q"), is to change the date reference from May 5, 2017 to May 4, 2017 on the Signatures page and on the certifications filed as Exhibits 31.1, 31.2, 32.1 and 32.2. No other changes have been made to the Form 10-Q. This Form 10-Q/A does not reflect events that may have occurred subsequent to the original filing date, and does not modify or update in any way disclosures made in the original Form 10-Q.