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v3.23.1

Summary of Significant Accounting Policies - Health Insurance (Details) $ in Thousands | 3 Months Ended
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Mar. 31, 2023 USD ($)
Accounting Policies [Abstract] |
Health insurance maximum risk of loss liability per employee insurance plan (up to) | $ 600
Health insurance maximum aggregate amount of risk of loss liability for employee insurance plans (up to) | $ 280

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- Definition Health Insurance Aggregate Risk Of Loss Liability Amount In Excess Of The Stop Loss Maximum + References No definition available. + Details
Name: | kfrc_HealthInsuranceAggregateRiskOfLossLiabilityAmountInExcessOfTheStopLossMaximum
Namespace Prefix: | kfrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Health Insurance, Stop Loss Maximum Per Claim + References No definition available. + Details
Name: | kfrc_HealthInsuranceStopLossMaximumPerClaim
Namespace Prefix: | kfrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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