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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)

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- Definition Gain or (Loss) on remeasurement Of Contingent Consideration + References No definition available. + Details
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Namespace Prefix: | fcn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration