LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loan modifications categorized as TDRs (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2022 USD ($) loan	Sep. 30, 2022 USD ($) loan
Number of contracts	1	2
Pre-Modification Outstanding Recorded Investment	$ 134,000	$ 481,000
Post-Modification Outstanding Recorded Investment	143,000	515,000
Recorded Investment	$ 143,000	$ 507,000
commercial real estate
Number of contracts	1	2
Pre-Modification Outstanding Recorded Investment	$ 134,000	$ 481,000
Post-Modification Outstanding Recorded Investment	143,000	515,000
Recorded Investment	$ 143,000	$ 507,000

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

No definition available.

+ Details

Name:	fkys_ReceivableChangeInMethodOfCalculatingImpairmentRecordedInvestment
Namespace Prefix:	fkys_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: