Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Credit Loss [Abstract]
Amount unrelated to trade receivables included in allowance	$ 0.6	$ 0.6

Accounts Receivable, Allowance For Credit Loss, Allowance Unrelated To Trade Receivables

No definition available.

Name:	kfrc_AccountsReceivableAllowanceForCreditLossAllowanceUnrelatedToTradeReceivables
Namespace Prefix:	kfrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant