Acquisition Accounting Valuation Discount on Covered Loans

No definition available.

Name:	colb_AcquisitionAccountingValuationDiscountOnCoveredLoans
Namespace Prefix:	colb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loans Receivable Real Estate Construction

+ References

No definition available.

+ Details

Name:	colb_LoansReceivableRealEstateConstruction
Namespace Prefix:	colb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loans Receivable Real Estate Mortgage.

+ References

No definition available.

+ Details

Name:	colb_LoansReceivableRealEstateMortgage
Namespace Prefix:	colb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Definition

Amount before allowance of loans issued to build, improve or remodel a residential home. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

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

- Definition

Amount before allowance of consumer mortgage. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes subordinated loans such as home equity lines of credit and loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(a)(3),(b))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount before allowance of consumer loans and leases not otherwise specified in the taxonomy. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

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

- Definition

Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=84165051&loc=d3e45377-112738

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159169&loc=d3e10152-111534

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

+ Details

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

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount before allowance of loans issued to commercial and industrial institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes real estate loans and loans covered under loss sharing agreements.

+ References

+ Details

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

- Definition

Amount before allowance of commercial construction loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5066-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(a)(2))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount before allowance of mortgage loans on existing land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5066-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(a)(3))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

+ Details

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

- Details

Name:	colb_LoansByMajorCategoryAxis=colb_LoansExcludingPurchasedCreditImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	colb_LoansByMajorCategoryAxis=colb_PurchasedCreditImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

Loans (Analysis of Loan Portfolio by Major Types of Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Less: unearned income on loans	$ (45,430)		$ (52,111)
Recorded Investment	8,454,107		8,358,657
Allowance for loan losses	(80,150)	$ (79,827)	(75,646)	$ (72,984)	$ (71,021)	$ (70,043)
Loans, net	8,373,957		8,283,011
Loans held for sale	6,773		5,766
Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Less: unearned income on loans	(45,430)		(52,111)
Recorded Investment	8,352,325		8,245,987
Allowance for loan losses	(75,368)		(68,739)
Loans, net	8,276,957		8,177,248
Loans held for sale	6,773		5,766
Loans and Leases Receivable, Gross	8,352,325		8,245,987
Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Less: unearned income on loans	0		0
Recorded Investment	101,782		112,670
Allowance for loan losses	(4,782)		(6,907)
Loans, net	97,000		105,763
Loans held for sale	0		0
Loans and Leases Receivable, Gross	109,175		120,758
Acquisition Accounting Valuation Discount on Covered Loans	7,393		8,088
Commercial and Multifamily Residential Construction [Domain] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	557		595
One-to-Four Family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross, Consumer, Mortgage	190,722		200,791
Loans and Leases Receivable, Gross, Consumer, Construction	206,346		200,695
Allowance for loan losses	(461)	(558)	(701)	(628)	(645)	(599)
One-to-Four Family Residential [Member] \| Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross, Consumer, Mortgage	180,522		188,396
Loans and Leases Receivable, Gross, Consumer, Construction	206,181		200,518
Loans and Leases Receivable, Gross	178,814		186,554
One-to-Four Family Residential [Member] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross, Consumer, Mortgage	10,200		12,395
Loans and Leases Receivable, Gross, Consumer, Construction	165		177
Loans and Leases Receivable, Gross	12,202		14,610
Commercial and Multifamily Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	3,826,506		3,901,333
Loans Receivable, Gross, Commercial, Construction	388,522		372,538
Commercial and Multifamily Residential [Member] \| Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	3,758,207		3,825,739
Loans Receivable, Gross, Commercial, Construction	387,951		371,931
Commercial and Multifamily Residential [Member] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Mortgage	68,299		75,594
Loans Receivable, Gross, Commercial, Construction	571		607
Loans and Leases Receivable, Gross	72,019		79,211
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial and Industrial	3,550,750		3,389,952
Commercial Portfolio Segment [Member] \| Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial and Industrial	3,538,492		3,377,324
Commercial Portfolio Segment [Member] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial and Industrial	12,258		12,628
Loans and Leases Receivable, Gross	12,921		13,753
Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Real Estate Mortgage	4,017,228		4,102,124
Real Estate Portfolio Segment [Member] \| Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Real Estate Mortgage	3,938,729		4,014,135
Real Estate Portfolio Segment [Member] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Real Estate Mortgage	78,499		87,989
Loans and Leases Receivable, Gross	84,221		93,821
One-to-Four Family Residential Construction [Domain] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	166		177
Real Estate Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Real Estate Construction	594,868		573,233
Real Estate Construction Portfolio Segment [Member] \| Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Real Estate Construction	594,132		572,449
Real Estate Construction Portfolio Segment [Member] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable Real Estate Construction	736		784
Loans and Leases Receivable, Gross	723		772
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross, Consumer	336,691		345,459
Allowance for loan losses	(5,292)	$ (5,216)	(5,163)	$ (3,551)	$ (3,360)	$ (3,534)
Consumer Portfolio Segment [Member] \| Loans, Excluding Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross, Consumer	326,402		334,190
Loans and Leases Receivable, Gross	325,158		332,225
Consumer Portfolio Segment [Member] \| Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Gross, Consumer	10,289		11,269
Loans and Leases Receivable, Gross	$ 11,310		$ 12,412