Loans, Impaired Financing Receivable (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	$ 18,121		$ 18,121		$ 19,050
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	12,158		12,158		13,047
Recorded Investment With Allowance	3,864		3,864		4,230
Total Recorded Investment	16,022		16,022		17,277
Related Allowance	269		269		510
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	16,210	$ 19,619	16,619	$ 19,589
Interest Income Recognized	94	143	192	278
Interest Income Recognized Cash Basis	8	0	15	2
Real Estate Loans [Member] \| Mortgages [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	766		766		1,070
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	574		574		740
Recorded Investment With Allowance	48		48		123
Total Recorded Investment	622		622		863
Related Allowance	9		9		9
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	718	1,062	784	1,047
Interest Income Recognized	3	5	8	10
Interest Income Recognized Cash Basis	0	0	0	0
Real Estate Loans [Member] \| Home Equity [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	103		103		150
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	40		40		70
Recorded Investment With Allowance	46		46		57
Total Recorded Investment	86		86		127
Related Allowance	7		7		9
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	109	142	117	144
Interest Income Recognized	2	1	3	3
Interest Income Recognized Cash Basis	0	0	0	0
Real Estate Loans [Member] \| Commercial [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	9,691		9,691		9,847
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	7,941		7,941		8,323
Recorded Investment With Allowance	903		903		860
Total Recorded Investment	8,844		8,844		9,183
Related Allowance	97		97		95
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	8,781	11,572	9,009	11,529
Interest Income Recognized	67	115	134	219
Interest Income Recognized Cash Basis	8	0	15	2
Real Estate Loans [Member] \| Agricultural [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	4,742		4,742		4,811
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	2,756		2,756		2,799
Recorded Investment With Allowance	1,734		1,734		1,846
Total Recorded Investment	4,490		4,490		4,645
Related Allowance	12		12		83
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	4,497	3,746	4,543	3,761
Interest Income Recognized	21	19	43	40
Interest Income Recognized Cash Basis	0	0	0	0
Consumer [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	0		0		2
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	0		0		2
Recorded Investment With Allowance	0		0		0
Total Recorded Investment	0		0		2
Related Allowance	0		0		0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	0	2	1	3
Interest Income Recognized	0	0	0	0
Interest Income Recognized Cash Basis	0	0	0	0
Other Commercial Loans [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	1,572		1,572		1,908
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	832		832		1,094
Recorded Investment With Allowance	101		101		241
Total Recorded Investment	933		933		1,335
Related Allowance	35		35		170
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	1,023	1,805	1,072	1,822
Interest Income Recognized	0	1	1	2
Interest Income Recognized Cash Basis	0	0	0	0
Other Agricultural Loans [Member]
Impaired Financing Receivable [Abstract]
Unpaid Principal Balance	1,247		1,247		1,262
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment With No Allowance	15		15		19
Recorded Investment With Allowance	1,032		1,032		1,103
Total Recorded Investment	1,047		1,047		1,122
Related Allowance	109		109		$ 144
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment	1,082	1,290	1,093	1,283
Interest Income Recognized	1	2	3	4
Interest Income Recognized Cash Basis	$ 0	$ 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: