v2.4.0.6

Other Borrowings	12 Months Ended
	Dec. 31, 2011
Other Borrowings [Abstract]
Other Borrowings	Other Borrowings Securities Sold Under Agreements to Repurchase The Company has entered into wholesale repurchase agreements with certain brokers. At December 31, 2011, the Company held $25.0 million in wholesale repurchase agreements with an interest rate of 1.88%. Securities available for sale with a carrying amount of $28.9 million were pledged as collateral for the repurchase agreement borrowings. The broker holds the securities while the Company continues to receive the principal and interest payments from the securities. Upon maturity of the agreement, the pledged securities will be returned to the Company.

X

- Details

Name:	colb_OtherBorrowingsAbstract
Namespace Prefix:	colb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The entire disclosure for repurchase agreements (also known as repos), resale agreements (also known as reverse repurchase agreements or reverse repos), securities borrowed transactions, and securities loaned transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6862952&loc=d3e113969-111729



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 08

-Paragraph m



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 17

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(m))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

+ Details

Name:	us-gaap_RepurchaseAgreementsResaleAgreementsSecuritiesBorrowedAndSecuritiesLoanedDisclosureTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration