    <SEC-DOCUMENT>0000887343-20-000189-index.html : 20200723
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    <ACCEPTANCE-DATETIME>20200723161655
    ACCESSION NUMBER:		0000887343-20-000189
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		16
    CONFORMED PERIOD OF REPORT:	20200723
    ITEM INFORMATION:		Results of Operations and Financial Condition
    ITEM INFORMATION:		Other Events
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20200723
    DATE AS OF CHANGE:		20200723

    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:		201043822

    	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-20200723.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: colb-20200723.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.1
    <SEQUENCE>2
    <FILENAME>a991colb2q2020earnings.htm
    <DESCRIPTION>PRESS RELEASE - EARNINGS AND DIVIDEND
    <TEXT>
    Document 2 - file: a991colb2q2020earnings.htm

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    <DOCUMENT>
    <TYPE>EX-101.SCH
    <SEQUENCE>3
    <FILENAME>colb-20200723.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
    <TEXT>
    Document 3 - file: colb-20200723.xsd

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    <SEQUENCE>4
    <FILENAME>colb-20200723_cal.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION CALCULATION LINKBASE DOCUMENT
    <TEXT>
    Document 4 - file: colb-20200723_cal.xml

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    <FILENAME>colb-20200723_def.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION DEFINITION LINKBASE DOCUMENT
    <TEXT>
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    <SEQUENCE>6
    <FILENAME>colb-20200723_lab.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION LABEL LINKBASE DOCUMENT
    <TEXT>
    Document 6 - file: colb-20200723_lab.xml

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    <SEQUENCE>7
    <FILENAME>colb-20200723_pre.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE DOCUMENT
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    <FILENAME>cbsystemsolidbuga161.jpg
    <DESCRIPTION>LOGO
    <TEXT>
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    <TYPE>XML
    <SEQUENCE>9
    <FILENAME>colb-20200723_htm.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
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    Document 9 - RAW XML: colb-20200723_htm.xml

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    <SEQUENCE>10
    <FILENAME>R1.htm
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 10 - file: R1.htm

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    <DOCUMENT>
    <TYPE>EXCEL
    <SEQUENCE>11
    <FILENAME>Financial_Report.xlsx
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 11 - file: Financial_Report.xlsx

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    <DOCUMENT>
    <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
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
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    <TYPE>XML
    <SEQUENCE>14
    <FILENAME>FilingSummary.xml
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    <TEXT>
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    <DOCUMENT>
    <TYPE>JSON
    <SEQUENCE>17
    <FILENAME>MetaLinks.json
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 17 - file: MetaLinks.json

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    <DOCUMENT>
    <TYPE>ZIP
    <SEQUENCE>18
    <FILENAME>0000887343-20-000189-xbrl.zip
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
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