Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Gain (loss) on remeasurement of contingent consideration	$ 0.0	$ (0.7)	$ (1.4)

Gain or (Loss) on remeasurement Of Contingent Consideration

No definition available.

Name:	fcn_GainLossOnRemeasurementOfContingentConsideration
Namespace Prefix:	fcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration