LOANS AND RELATED ALLOWANCE FOR LOAN LOSSES, Impaired Financing Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	$ 17,905	$ 19,050
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	14,878	13,047
Recorded Investment With Allowance	655	4,230
Total Recorded Investment	15,533	17,277
Related Allowance	121	510
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	15,880	18,278	$ 21,294
Interest Income Recognized	395	468	558
Interest Income Recognized Cash Basis	31	27	24
Real Estate Loans [Member] \| Mortgages [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	697	1,070
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	495	740
Recorded Investment With Allowance	45	123
Total Recorded Investment	540	863
Related Allowance	6	9
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	682	956	1,062
Interest Income Recognized	16	20	16
Interest Income Recognized Cash Basis	0	0	0
Real Estate Loans [Member] \| Home Equity [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	97	150
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	37	70
Recorded Investment With Allowance	43	57
Total Recorded Investment	80	127
Related Allowance	6	9
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	99	139	119
Interest Income Recognized	4	6	6
Interest Income Recognized Cash Basis	0	0	0
Real Estate Loans [Member] \| Commercial [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	9,330	9,847
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	8,096	8,323
Recorded Investment With Allowance	285	860
Total Recorded Investment	8,381	9,183
Related Allowance	61	95
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	8,789	10,354	11,756
Interest Income Recognized	288	358	453
Interest Income Recognized Cash Basis	31	27	24
Real Estate Loans [Member] \| Agricultural [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	5,694	4,811
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	5,167	2,799
Recorded Investment With Allowance	188	1,846
Total Recorded Investment	5,355	4,645
Related Allowance	14	83
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	4,562	3,918	4,899
Interest Income Recognized	82	75	78
Interest Income Recognized Cash Basis	0	0	0
Consumer [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	0	2
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	0	2
Recorded Investment With Allowance	0	0
Total Recorded Investment	0	2
Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment		3	2
Interest Income Recognized		0	0
Interest Income Recognized Cash Basis		0	0
Other Commercial Loans [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	813	1,908
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	92	1,094
Recorded Investment With Allowance	94	241
Total Recorded Investment	186	1,335
Related Allowance	34	170
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	704	1,671	2,056
Interest Income Recognized	2	3	1
Interest Income Recognized Cash Basis	0	0	0
Other Agricultural Loans [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	1,274	1,262
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	991	19
Recorded Investment With Allowance	0	1,103
Total Recorded Investment	991	1,122
Related Allowance	0	144
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	1,044	1,237	1,400
Interest Income Recognized	3	6	4
Interest Income Recognized Cash Basis	$ 0	$ 0	$ 0

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestmentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalanceAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=czfs_AgriculturalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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