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v3.20.4

Fair Value Measurements - Summary of Changes in the Fair Value of Level 3 Contingent Consideration (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019
Fair Value Disclosures [Abstract] |  |
Consideration paid to sellers based on financial performance | $ 2.7 | $ 1.8

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- Definition Business combinations additional consideration paid to sellers. + References No definition available. + Details
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Namespace Prefix: | forr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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