v2.4.1.9

Business combinations (Details) (USD $) | 0 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Apr. 01, 2013 | Mar. 31, 2015 | Mar. 31, 2014 | Apr. 01, 2013
Business Acquisition [Line Items] |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired | 100.00%us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired |  |  | 100.00%us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Business Acquisition, Pro Forma Net Income (Loss) |  |  | $ 21,078,000 us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss |
West Coast Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Acquisition, Effective Date of Acquisition | Nov. 01, 2014 |  |  |
Business Acquisition, Cost of Acquired Entity, Purchase Price | 131,900,000 colb_BusinessCombinationCostofAcquiredEntityPurchasePriceTotal / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |  |  | 131,900,000 colb_BusinessCombinationCostofAcquiredEntityPurchasePriceTotal / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net | 93,400,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |  |  | 93,400,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember
Business Acquisition, Purchase Price Allocation, Liabilities, Deposits | (736,800,000)colb_BusinessCombinationPurchasePriceAllocationLiabilitiesDeposits / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |  |  | (736,800,000)colb_BusinessCombinationPurchasePriceAllocationLiabilitiesDeposits / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember
Business Combination, Acquired Receivables, Fair Value | 502,600,000 us-gaap_BusinessCombinationAcquiredReceivablesFairValue / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |  |  | 502,600,000 us-gaap_BusinessCombinationAcquiredReceivablesFairValue / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets | 10,900,000 colb_BusinessCombinationPurchasePriceAllocationAmortizableIntangibleAssets / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |  |  | 10,900,000 colb_BusinessCombinationPurchasePriceAllocationAmortizableIntangibleAssets / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember
Business Acquisition, Purchase Price Allocation, Goodwill Amount | 38,600,000 colb_BusinessCombinationPurchasePriceAllocationGoodwillAmount / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |  |  | 38,600,000 colb_BusinessCombinationPurchasePriceAllocationGoodwillAmount / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember
Business Acquisition, Pro Forma Revenue |  |  | 97,488,000 us-gaap_BusinessAcquisitionsProFormaRevenue / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |
Business Acquisition, Pro Forma Earnings Per Share, Basic |  |  | $ 0.38 us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |
Business Acquisition, Pro Forma Earnings Per Share, Diluted |  |  | $ 0.37 us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |
Business Combination, Acquisition Related Costs |  | 72,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember | 966,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_WestCoastBancorpMember |
Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | 2,902,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember |  |
Compensation and employee benefits [Member] | Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | 273,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember / us-gaap_IncomeStatementLocationAxis = colb_CompensationandemployeebenefitsMember |  |
Occupancy [Member] | Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | 499,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember / us-gaap_IncomeStatementLocationAxis = colb_OccupancyMember |  |
Advertising and promotion [Member] | Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | 96,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember / us-gaap_IncomeStatementLocationAxis = colb_AdvertisingandpromotionMember |  |
Data processing and communications [Member] | Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | 1,558,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember / us-gaap_IncomeStatementLocationAxis = colb_DataprocessingandcommunicationsMember |  |
Legal and professional fees [Member] | Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | 385,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember / us-gaap_IncomeStatementLocationAxis = colb_LegalandprofessionalfeesMember |  |
Other noninterest expenses [Member] | Intermountain Community Bancorp [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  | $ 91,000 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = colb_IntermountainCommunityBancorpMember / us-gaap_IncomeStatementLocationAxis = colb_OthernoninterestexpensesMember |  |

X
- Definition The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition. + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Combination, Purchase Price Allocation Amortizable Intangible Assets + References No definition available. + Details
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Namespace Prefix: | colb_
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 No definition available. + Details
Name: | colb_BusinessCombinationPurchasePriceAllocationGoodwillAmount
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Data Type: | xbrli:monetaryItemType
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Period Type: | instant

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- Definition Business Combination, Purchase Price Allocation, Liabilities, Deposits + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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- Definition Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format. + References Reference 1: 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=34752592&loc=d3e845-128460 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Acquisition Date -URI http://asc.fasb.org/extlink&oid=6919109 Reference 3: 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=34752592&loc=d3e848-128460 Reference 4: 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=25497992&loc=d3e1392-128463 + Details
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- Details
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- Definition Percentage of voting equity interests acquired at the acquisition date in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(2)-(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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Balance Type: | na
Period Type: | duration

X
- Definition The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(2)-(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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Balance Type: | na
Period Type: | duration

X
- Definition The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(2)-(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(2)-(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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=39739317&loc=d3e4845-128472 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e1043-128460 + Details
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- Definition Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed. + 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 (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464 + Details
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- Details
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- Details
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Data Type: | na
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- Details
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- Details
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- Details
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