v2.4.0.6

Business Combinations (Narrative) (Details) (USD $) | 7 Months Ended | 12 Months Ended | 0 Months Ended |  | 0 Months Ended |  | 0 Months Ended |  | 0 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2011 location | Dec. 31, 2011 location | Dec. 31, 2011 location | Dec. 31, 2010 | Dec. 31, 2009 | Aug. 05, 2011 Bank of Whitman [Member] location | Dec. 31, 2011 Bank of Whitman [Member] location | May 27, 2011 First Heritage Bank [Member] location years | Dec. 31, 2011 First Heritage Bank [Member] | May 20, 2011 First Heritage Bank [Member] Maximum [Member] | May 20, 2011 Summit Bank [Member] years | Dec. 31, 2011 Summit Bank [Member] | May 20, 2011 Summit Bank [Member] Maximum [Member] | May 27, 2011 Scenario, Previously Reported [Member] First Heritage Bank [Member] | May 20, 2011 Scenario, Previously Reported [Member] Summit Bank [Member]
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition date |  |  |  |  |  | August 5, 2011 |  | May 27, 2011 |  |  | May 20, 2011 |  |  |  |
Number Of Branch Locations To Be Acquired |  |  |  |  |  | 9 |  | 5 |  |  |  |  |  |  |
Bargain purchase gain, net of tax |  |  | $ 1,830,000 | $ 9,818,000 | $ 0 | $ 1,830,000 |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  | 4,023,000 |  |  | 1,892,000 |  |  |  |
Core deposit intangible |  |  |  |  |  | 3,943,000 |  | 1,337,000 |  |  | 509,000 |  |  |  |
Business Acquisition, Purchase Price Allocation, Goodwill, Expected Tax Deductible Amount |  |  |  |  |  |  |  | 4,023,000 |  |  | 1,892,000 |  |  |  |
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets, Expected Tax Deductible Amount |  |  |  |  |  | 3,943,000 |  | 1,337,000 |  |  | 509,000 |  |  |  |
Number Of Branch Locations Excluded From Operating Results |  |  |  |  |  |  | 11 |  |  |  |  |  |  |  |
Percentage of loss shared by FDIC |  |  |  |  |  |  |  |  | 80.00% |  |  | 80.00% |  |  |
FDIC Percentage Of Loss Recoveries |  |  |  |  |  |  |  |  | 80.00% |  |  | 80.00% |  |  |
Term of loss sharing agreements for commercial loans |  |  |  |  |  |  |  | 5 |  |  | 5 |  |  |  |
Term of Loss sharing agreements for Single family residential mortgage loans |  |  |  |  |  |  |  | 10 |  |  | 10 |  |  |  |
Commercial Loans Period Of Loss Recovery Provisions |  |  |  |  |  |  |  | 8 |  |  | 8 |  |  |  |
Single Family Residential Mortgage Loans Period of Loss Recovery Provisions |  |  |  |  |  |  |  | 10 |  |  | 10 |  |  |  |
FDIC Indemnification Asset, Accrued Interest On Loans, Period of Accrual |  |  |  |  |  |  |  |  |  | 90 days |  |  | 90 days |  |
Number Of Branch Locations | 102 | 102 | 102 |  |  |  |  |  |  |  |  |  |  |  |
Acquired loans |  |  |  |  |  | 200,041,000 |  | 81,488,000 |  |  | 69,783,000 |  |  | 81,900,000 | 71,400,000
Other real estate owned covered by loss sharing |  |  |  |  |  |  |  | 8,225,000 |  |  | 2,162,000 |  |  | 8,300,000 | 2,700,000
FDIC indemnification asset |  |  |  |  |  |  |  | 38,531,000 |  |  | 30,203,000 |  |  | 38,100,000 | 27,200,000
Other assets |  |  |  |  |  | 2,447,000 |  | 3,657,000 |  |  | 1,813,000 |  |  | 1,700,000 | 786,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Acquired Loans | 369,000 | 1,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Loans Covered By Loss Sharing | 61,000 | 509,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, FDIC Indemnification Asset | 427,000 | 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Assets | $ 1,900,000 | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition The amount of amortizable intangible assets arising from a business combination that is expected to be deductible for tax purposes. + References No definition available. + Details
Name: | colb_BusinessAcquisitionPurchasePriceAllocationAmortizableIntangibleAssetsExpectedTaxDeductibleAmount
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Acquisition, Purchase Price Allocation, FDIC Indemnification Asset + References No definition available. + Details
Name: | colb_BusinessAcquisitionPurchasePriceAllocationFdicIndemnificationAsset
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Acquisition, Purchase Price Allocation, Loans Covered By Loss Sharing + References No definition available. + Details
Name: | colb_BusinessAcquisitionPurchasePriceAllocationLoansCoveredByLossSharing
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Acquisition, Purchase Price Allocation, Other Assets + References No definition available. + Details
Name: | colb_BusinessAcquisitionPurchasePriceAllocationOtherAssets
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Acquired Loans + References No definition available. + Details
Name: | colb_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAcquiredLoans
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, FDIC Indemnification Asset + References No definition available. + Details
Name: | colb_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFdicIndemnificationAsset
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Loans Covered By Loss Sharing + References No definition available. + Details
Name: | colb_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLoansCoveredByLossSharing
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Assets + References No definition available. + Details
Name: | colb_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherAssets
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Commercial Loans Period Of Loss Recovery Provisions. + References No definition available. + Details
Name: | colb_CommercialLoansPeriodOfLossRecoveryProvisions
Namespace Prefix: | colb_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

X
- Definition FDIC Indemnification Asset, Accrued Interest On Loans, Period of Accrual + References No definition available. + Details
Name: | colb_FdicIndemnificationAssetAccruedInterestOnLoansPeriodOfAccrual
Namespace Prefix: | colb_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition FDIC Percentage Of Loss Recoveries + References No definition available. + Details
Name: | colb_FdicPercentageOfLossRecoveries
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number Of Branch Locations + References No definition available. + Details
Name: | colb_NumberOfBranchLocations
Namespace Prefix: | colb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number Of Branch Locations Excluded From Operating Results + References No definition available. + Details
Name: | colb_NumberOfBranchLocationsExcludedFromOperatingResults
Namespace Prefix: | colb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number Of Branch Locations To Be Acquired + References No definition available. + Details
Name: | colb_NumberOfBranchLocationsToBeAcquired
Namespace Prefix: | colb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of loss shared by FDIC + References No definition available. + Details
Name: | colb_PercentageOfLossSharedByFdic
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Single Family Residential Mortgage Loans Period of Loss Recovery Provisions. + References No definition available. + Details
Name: | colb_SingleFamilyResidentialMortgageLoansPeriodOfLossRecoveryProvisions
Namespace Prefix: | colb_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Term of Loss sharing agreements for commercial loans + References No definition available. + Details
Name: | colb_TermOfLossSharingAgreementsForCommercialLoans
Namespace Prefix: | colb_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Term of Loss sharing agreements for Single family residential mortgage loans + References No definition available. + Details
Name: | colb_TermOfLossSharingAgreementsForSingleFamilyResidentialMortgageLoans
Namespace Prefix: | colb_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Month, date and year in which the acquirer obtains control of the acquiree. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6909708&loc=d3e848-128460 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6909870&loc=d3e1392-128463 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 3 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6909708&loc=d3e845-128460 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 10, 11 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 68 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Acquisition Date -URI http://asc.fasb.org/extlink&oid=6919109 + Details
Name: | us-gaap_BusinessAcquisitionEffectiveDateOfAcquisition
Namespace Prefix: | us-gaap_
Data Type: | us-types:dateStringItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition The amount of acquisition cost of a business combination allocated to an identifiable intangible asset that will be amortized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 51 -Subparagraph e -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 52 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_BusinessAcquisitionPurchasePriceAllocationAmortizableIntangibleAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 52 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 53 -Subparagraph d -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6911361&loc=d3e6927-128479 -Subparagraph (d) Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 52 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 53 -Subparagraph d -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 68 -Subparagraph k -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the fair value of the receivables acquired, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 68 -Subparagraph h(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 03-3 -Paragraph 3 -Subparagraph a-g -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 6 -Subparagraph b(ii) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_BusinessCombinationAcquiredReceivablesFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 25 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6396-128476 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 36, 37, 38 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6571-128477 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141R -Paragraph 68 -Subparagraph o(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=6911361&loc=d3e6927-128479 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6387-128476 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6527-128477 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 25 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6393-128476 + Details
Name: | us-gaap_BusinessCombinationBargainPurchaseGainRecognizedAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration