v2.4.1.9

Shareholders' Equity Narrative (Details) | Mar. 31, 2015
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Shareholders' Equity [Abstract] |
Preferred Stock Converted Into Common Stock, Shares | 102,363 colb_PreferredStockConvertedIntoCommonStockShares

X
- Definition Preferred Stock Converted Into Common Stock, Shares + References No definition available. + Details
Name: | colb_PreferredStockConvertedIntoCommonStockShares
Namespace Prefix: | colb_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | colb_ShareholdersEquityAbstract
Namespace Prefix: | colb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration