Business Combination, Purchase Price Allocation, Junior Subordinated Debentures

No definition available.

Name:	colb_BusinessCombinationPurchasePriceAllocationJuniorSubordinatedDebentures
Namespace Prefix:	colb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Junior subordinated debt (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
Junior subordinated debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Nov. 01, 2017
Junior subordinated debentures [Line Items]
Repayments of junior subordinated debt	$ 0	$ 8,248	$ 6,200
Pacific Continental [Member]
Junior subordinated debentures [Line Items]
Business Combination, Purchase Price Allocation, Junior Subordinated Debentures				$ 14,400