v2.4.1.9

Shareholders' Equity (Details) (USD $) | 0 Months Ended
--- | ---
Jan. 29, 2015 | Apr. 22, 2015 | Apr. 01, 2013
Subsequent Event [Line Items] |  |  |
Declared quarterly cash dividend | $ 0.16 us-gaap_CommonStockDividendsPerShareDeclared |  |
Special Dividends Payable, Amount Per Share | $ 0.14 colb_SpecialDividendsPayableAmountPerShare |  |
Dividend Declared [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Declared quarterly cash dividend |  | $ 0.18 us-gaap_CommonStockDividendsPerShareDeclared / us-gaap_SubsequentEventTypeAxis = us-gaap_DividendDeclaredMember |
Special Dividends Payable, Amount Per Share |  | $ 0.16 colb_SpecialDividendsPayableAmountPerShare / us-gaap_SubsequentEventTypeAxis = us-gaap_DividendDeclaredMember |
Preferred Stock [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Stock Issued During Period, Shares, New Issues |  |  | 8,782 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_PreferredStockMember

X
- Definition Special Dividends Payable, Amount Per Share + References No definition available. + Details
Name: | colb_SpecialDividendsPayableAmountPerShare
Namespace Prefix: | colb_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of new stock issued during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
Name: | us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_PreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_DividendDeclaredMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |