Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 4,152,729	$ 3,195,732
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	429,211	43,236
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	696,596	383,754
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	97,447	14,645
Debt Securities, Available-for-sale, Unrealized Loss Position	4,849,325	3,579,486
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	526,658	57,881
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,595,623	2,292,062
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	249,339	30,777
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	390,944	176,946
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	60,175	7,315
Debt Securities, Available-for-sale, Unrealized Loss Position	2,986,567	2,469,008
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	309,514	38,092
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	265,060	195,708
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	23,946	4,823
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	114,909	117,751
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	15,534	4,968
Debt Securities, Available-for-sale, Unrealized Loss Position	379,969	313,459
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	39,480	9,791
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	708,006	237,354
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	98,857	3,862
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	73,417	40,343
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	12,514	1,076
Debt Securities, Available-for-sale, Unrealized Loss Position	781,423	277,697
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	111,371	4,938
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	87,960	100,813
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,781	1,988
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	117,326	48,714
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9,224	1,286
Debt Securities, Available-for-sale, Unrealized Loss Position	205,286	149,527
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	11,005	3,274
US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	171,319	157,536
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11,362	831
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	171,319	157,536
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	11,362	831
Non-agency collateralized mortgage obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	324,761	212,259
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	43,926	955
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	324,761	212,259
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 43,926	$ 955

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI https://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI https://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI https://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456

+ Details

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

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=colb_USGovernmentAgencyAndGovernmentSponsoredEnterpriseMortgageBackedSecuritiesAndCollateralizedMortgageObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: