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Shareholders' Equity Dividends Declared (Tables) | 3 Months Ended
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Mar. 31, 2020
Shareholders' Equity [Abstract] |
Dividends Declared [Table Text Block] | The following table summarizes year-to-date dividend activity as of March 31, 2020:
Declared |  | Regular Cash Dividends Per Common Share |  | Special Cash Dividends Per Common Share |  | Record Date |  | Paid Date
January 23, 2020 |  | $ | 0.28 |  |  | $ | 0.22 |  |  | February 5, 2020 |  | February 19, 2020

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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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- Definition Tabular disclosure of information related to dividends declared, including paid and unpaid dividends. + References No definition available. + Details
Name: | us-gaap_DividendsDeclaredTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration