XML 102 R76.htm IDEA: XBRL DOCUMENT
v3.20.4

Allowance for Credit Losses and Unfunded Commitments and Letters of Credit (Narrative) (Details) | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Minimum loan balance of nonaccrual, collateral dependent loans considered for ACL | $ 500,000
Allowance for Credit Loss, Period Increase (Decrease) | $ 63,500,000

X
- Definition Minimum loan balance of nonaccrual, collateral dependent loans considered for ACL + References No definition available. + Details
Name: | colb_MinimumloanbalanceofnonaccrualcollateraldependentloansconsideredforACL
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of increase (decrease) in allowance for credit loss on financing receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration