Securities Sold Under Agreements to Repurchase (Details) - Repurchase Agreements, Sweep $ in Millions	Dec. 31, 2021 USD ($)
Assets Sold under Agreements to Repurchase [Line Items]
Carrying amount of securities pledged as collateral	$ 101.1
Available-for-sale Securities
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Sweep, Carrying Amount	$ 86.0
Assets Sold under Agreements to Repurchase, Sweep, Interest rate	0.18%

Carrying amount of assets sold under agreements to repurchase related to sweep products when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets.

No definition available.

+ Details

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

- Definition

Interest rate on the amount to be repaid to the counterparty to the sweep product repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

+ References

No definition available.

+ Details

Name:	colb_AssetsSoldunderAgreementstoRepurchaseSweepInterestrate
Namespace Prefix:	colb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

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

- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: