Revolving Line of Credit	9 Months Ended
	Sep. 30, 2020
Line of Credit [Member]
Line of Credit Facility [Line Items]
Short-term Debt [Text Block]	Revolving Line of CreditThe Company has a $15.0 million short-term credit facility with an unaffiliated bank that expires May 27, 2021. This facility has a variable interest rate and provides the Company additional liquidity, if needed, for various corporate activities including the repurchase of shares of Columbia Banking System, Inc. common stock. There was no outstanding balance at both September 30, 2020 and December 31, 2019. The credit agreement requires the Company to comply with certain covenants including those related to asset quality and capital levels. The Company was in compliance with all covenants associated with this facility at September 30, 2020.