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