Summary of Significant Accounting Policies - Health Insurance (Details)	12 Months Ended
Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Health insurance maximum risk of loss liability per employee insurance plan (up to)	$ 350,000
Health insurance maximum aggregate amount of risk of loss liability for employee insurance plans (up to)	$ 700,000

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