Business (Details) - Minority Stock Offering	Apr. 19, 2018 shares
Columbia Bank, MHC
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)	62,580,155
Columbia Bank Foundation
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)	3,476,675
Columbia Bank Employee Stock Ownership Plan
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)	49,832,345