Note 21 - Fair Value Measurements and Fair Values of Financial Instruments - Estimated Fair Values, and Related Carrying Amounts, of the Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Reported Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	$ 31,122	$ 32,827
Reported Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Certificates of deposit	4,080	4,660
Restricted equity securities (included in Other Assets)	10,321	5,712
Accrued interest receivable	5,001	3,968
Short-term borrowings	86,220	12,853
Long-term borrowings	52,127	35,915
Accrued interest payable	311	142
Reported Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Deposits With No Stated Maturity [Member]
Deposits, fair value	877,965	804,207
Reported Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Time Deposits [Member]
Deposits, fair value	374,695	229,565
Reported Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Loans, net	1,172,386	818,254
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	31,122	32,827
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Certificates of deposit	4,227	4,634
Restricted equity securities (included in Other Assets)	10,321	5,712
Accrued interest receivable	5,001	3,968
Short-term borrowings	86,166	12,617
Long-term borrowings	52,040	35,902
Accrued interest payable	311	142
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Deposits With No Stated Maturity [Member]
Deposits, fair value	877,965	804,207
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Time Deposits [Member]
Deposits, fair value	376,738	229,751
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Loans, net	$ 1,181,000	$ 825,809

Represents the fair value portion of accrued interest payable.

No definition available.

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Namespace Prefix:	cznc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value of Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

+ References

No definition available.

+ Details

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Namespace Prefix:	cznc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value disclosure of a savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

No definition available.

+ Details

Name:	cznc_CertificatesOfDepositFairValueDisclosure
Namespace Prefix:	cznc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The aggregate value of all restricted investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-12C.9(c))
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.6(c))
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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