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Summary of Significant Accounting Policies - Trade Receivables and Related Reserves (Details)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Accounts receivable reserves as percentage of gross accounts receivable	1.00%	1.00%

X

- Definition

Accounts receivable reserves as percentage of gross accounts receivable.

+ References

No definition available.

+ Details

Name:	kfrc_AccountsReceivableReservesAsPercentageOfGrossAccountsReceivable
Namespace Prefix:	kfrc_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
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