    <SEC-DOCUMENT>0000887343-20-000203-index.html : 20201029
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    <ACCEPTANCE-DATETIME>20201029164503
    ACCESSION NUMBER:		0000887343-20-000203
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		16
    CONFORMED PERIOD OF REPORT:	20201029
    ITEM INFORMATION:		Results of Operations and Financial Condition
    ITEM INFORMATION:		Other Events
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20201029
    DATE AS OF CHANGE:		20201029

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			COLUMBIA BANKING SYSTEM, INC.
    		CENTRAL INDEX KEY:			0000887343
    		STANDARD INDUSTRIAL CLASSIFICATION:	STATE COMMERCIAL BANKS [6022]
    		IRS NUMBER:				911422237
    		STATE OF INCORPORATION:			WA
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-20288
    		FILM NUMBER:		201273220

    	BUSINESS ADDRESS:
    		STREET 1:		1301 A STREET
    		CITY:			TACOMA
    		STATE:			WA
    		ZIP:			98402
    		BUSINESS PHONE:		2533051900

    	MAIL ADDRESS:
    		STREET 1:		1301 A STREET
    		CITY:			TACOMA
    		STATE:			WA
    		ZIP:			98402

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	COLUMBIA BANKING SYSTEM INC
    		DATE OF NAME CHANGE:	19930328
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>colb-20201029.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: colb-20201029.htm

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    <SEQUENCE>2
    <FILENAME>a991colb3q2020earnings.htm
    <DESCRIPTION>PRESS RELEASE - EARNINGS AND DIVIDEND
    <TEXT>
    Document 2 - file: a991colb3q2020earnings.htm

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    <DOCUMENT>
    <TYPE>EX-101.SCH
    <SEQUENCE>3
    <FILENAME>colb-20201029.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
    <TEXT>
    Document 3 - file: colb-20201029.xsd

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    <FILENAME>colb-20201029_cal.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION CALCULATION LINKBASE DOCUMENT
    <TEXT>
    Document 4 - file: colb-20201029_cal.xml

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    <FILENAME>colb-20201029_def.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION DEFINITION LINKBASE DOCUMENT
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    <SEQUENCE>6
    <FILENAME>colb-20201029_lab.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION LABEL LINKBASE DOCUMENT
    <TEXT>
    Document 6 - file: colb-20201029_lab.xml

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    <FILENAME>cbsystemsolidbuga161.jpg
    <DESCRIPTION>LOGO
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    <FILENAME>colb-20201029_pre.xml
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    <TEXT>
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    <DESCRIPTION>IDEA: XBRL DOCUMENT
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    <FILENAME>R1.htm
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    <TEXT>
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    <TYPE>EXCEL
    <SEQUENCE>11
    <FILENAME>Financial_Report.xlsx
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 11 - file: Financial_Report.xlsx

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    <TYPE>XML
    <SEQUENCE>12
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    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 12 - file: Show.js

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    <SEQUENCE>13
    <FILENAME>report.css
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    <TEXT>
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    <TYPE>XML
    <SEQUENCE>14
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    <TEXT>
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    <TYPE>JSON
    <SEQUENCE>16
    <FILENAME>MetaLinks.json
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 16 - file: MetaLinks.json

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    <DOCUMENT>
    <TYPE>ZIP
    <SEQUENCE>17
    <FILENAME>0000887343-20-000203-xbrl.zip
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
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