Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Summary of investment securities
Available-for-sale Securities, Amortized Cost	$ 169,501	$ 183,625
Available-for-sale Securities, Gross Unrealized Gains	515	618
Available-for-sale Securities, Gross Unrealized Losses	4,917	5,024
Available-for-sale securities, Fair Value	165,099	179,219
U.S. Government agencies and corporations
Summary of investment securities
Available-for-sale Securities, Amortized Cost	8,170	8,165
Available-for-sale Securities, Gross Unrealized Gains	25	3
Available-for-sale Securities, Gross Unrealized Losses	182	180
Available-for-sale securities, Fair Value	8,013	7,988
Obligations of states and political subdivisions
Summary of investment securities
Available-for-sale Securities, Amortized Cost	63,847	68,219
Available-for-sale Securities, Gross Unrealized Gains	460	582
Available-for-sale Securities, Gross Unrealized Losses	1,909	2,031
Available-for-sale securities, Fair Value	62,398	66,770
U.S. Government-sponsored mortgage-backed securities
Summary of investment securities
Available-for-sale Securities, Amortized Cost	74,307	81,281
Available-for-sale Securities, Gross Unrealized Gains	30	32
Available-for-sale Securities, Gross Unrealized Losses	1,516	1,546
Available-for-sale securities, Fair Value	72,821	79,767
U.S. Government-sponsored collateralized mortgage obligations
Summary of investment securities
Available-for-sale Securities, Amortized Cost	7,425	9,504
Available-for-sale Securities, Gross Unrealized Losses	126	155
Available-for-sale securities, Fair Value	7,299	9,349
U.S. Government-guaranteed small business administration pools
Summary of investment securities
Available-for-sale Securities, Amortized Cost	11,552	12,255
Available-for-sale Securities, Gross Unrealized Gains		1
Available-for-sale Securities, Gross Unrealized Losses	392	317
Available-for-sale securities, Fair Value	11,160	11,939
Trust preferred securities
Summary of investment securities
Available-for-sale Securities, Amortized Cost	1,619	1,620
Available-for-sale Securities, Gross Unrealized Losses	792	795
Available-for-sale securities, Fair Value	827	825
Total debt securities
Summary of investment securities
Available-for-sale Securities, Amortized Cost	166,920	181,044
Available-for-sale Securities, Gross Unrealized Gains	515	618
Available-for-sale Securities, Gross Unrealized Losses	4,917	5,024
Available-for-sale securities, Fair Value	162,518	176,638
Federal Home Loan Bank (FHLB) stock
Summary of investment securities
Available-for-sale Securities, Amortized Cost	2,355	2,355
Available-for-sale securities, Fair Value	2,355	2,355
Federal Reserve Bank (FRB) stock
Summary of investment securities
Available-for-sale Securities, Amortized Cost	226	226
Available-for-sale securities, Fair Value	226	226
Total regulatory stock
Summary of investment securities
Available-for-sale Securities, Amortized Cost	2,581	2,581
Available-for-sale securities, Fair Value	$ 2,581	$ 2,581

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

+ Details

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

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

+ Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cldb_USGovernmentGuaranteedSmallBusinessAdministrationPoolsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cldb_TrustPreferredSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cldb_FederalHomeLoanBankStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cldb_FederalReserveBankStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cldb_RegulatoryStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: