Share Repurchase Program - Additional Information (Details)	Sep. 30, 2018 USD ($)
Equity [Abstract]
Stock repurchase program, authorized amount	$ 100,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 91,400,000
Line of credit facility, conditions for the elimination of limits on shares repurchases, leverage ratio	3.25

The maximum leverage ratio requirement that represents a condition for the elimination of limits on share repurchases, with regard to credit facility covenants.

No definition available.

Name:	icfi_LineOfCreditFacilityConditionsForTheEliminationOfLimitsOnSharesRepurchasesLeverageRatio
Namespace Prefix:	icfi_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant