Other Real Estate Owned (Summary of Other Real Estate Owned) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021
Other Real Estate Owned [Line Items]
Balance, beginning of period	$ 381	$ 553
Valuation adjustments	(182)	(140)
Proceeds from Sale of OREO property	(200)	(132)
Gain on sale of OREO, net	1	100
Balance, end of period	0	$ 381
Real estate: One-to-four family residential
Other Real Estate Owned [Line Items]
Balance, end of period	$ 0

Other Real Estate Owned [Line Items]

No definition available.

Name:	colb_OtherRealEstateOwnedLineItems
Namespace Prefix:	colb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Transfer Other Real Estate Write Down

+ References

No definition available.

+ Details

Name:	colb_TransferOtherRealEstateWriteDown
Namespace Prefix:	colb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net gain (loss) resulting from sales and other disposals of other real estate owned, increases (decreases) in the valuation allowance for foreclosed real estate, and write-downs of other real estate owned after acquisition or physical possession.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14(d))
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

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

- Definition

The cash inflow from proceeds From Sales of Wholly Owned Real Estate and Real Estate Acquired in Settlement of Loans.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585

+ Details

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

- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5162-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4437-111522

+ Details

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

- Details

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