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

Preferred Stock Converted Into Common Stock, Shares

No definition available.

Name:	colb_PreferredStockConvertedIntoCommonStockShares
Namespace Prefix:	colb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant