Summary of Significant Accounting Policies - Health Insurance (Details) $ in Thousands	9 Months Ended
Sep. 30, 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

Health Insurance Aggregate Risk Of Loss Liability Amount In Excess Of The Stop Loss Maximum

No definition available.

Name:	kfrc_HealthInsuranceAggregateRiskOfLossLiabilityAmountInExcessOfTheStopLossMaximum
Namespace Prefix:	kfrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration