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Allowance for Credit Losses - Additional Information (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Credit Loss [Abstract] |  |
Amount unrelated to trade receivables included in allowance | $ 0.5 | $ 0.6

X
- Definition Accounts Receivable, Allowance For Credit Loss, Allowance Unrelated To Trade Receivables + References No definition available. + Details
Name: | kfrc_AccountsReceivableAllowanceForCreditLossAllowanceUnrelatedToTradeReceivables
Namespace Prefix: | kfrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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