v2.4.0.6

Allowance for Noncovered Loan and Lease Losses and Unfunded Commitments and Letters of Credit (Narrative) (Details) (Maximum [Member]) | 12 Months Ended
--- | ---
Dec. 31, 2011
Maximum [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Percentage of unallocated loan amount | 5.00%

X
- Definition Unallocated Loan Amount As Percentage Of Allowance + References No definition available. + Details
Name: | colb_UnallocatedLoanAmountPercentageOfAllowance
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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