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Shareholders' Equity Narrative (Details) | Sep. 30, 2015 shares
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Shareholders' Equity [Abstract] |
Preferred Stock Converted Into Common Stock, Shares | 102,363

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- Definition Preferred Stock Converted Into Common Stock, Shares + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Shareholders' Equity [Abstract] + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | xbrli:stringItemType
Balance Type: | na
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