FAIR VALUE MEASUREMENTS - Additional Information (Details)	Jun. 30, 2021 USD ($)
FAIR VALUE MEASUREMENTS
Minimum impaired loan balance that requires an appraisal or certificate of inspection to be obtained and reviewed annually for impaired loan valuation procedure	$ 250,000
Maximum impaired loan balance for which the bank completes a Certificate of Inspection	$ 250,000

Impaired Loan Balance That Requires Appraisal or Certificate of Inspection For Impaired Loan Valuation Procedure.

No definition available.

Name:	fkys_ImpairedLoanBalanceThatRequireAppraisalOrCertificateOfInspectionForImpairedLoanValuationProcedure
Namespace Prefix:	fkys_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant