Business Combination, Purchase Price Allocation, Junior Subordinated Debentures

No definition available.

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

- Definition

Repayments of subordinated debt, Intermountain Statutory Trust

+ References

No definition available.

+ Details

Name:	colb_RepaymentsofsubordinateddebtIntermountainStatutoryTrust
Namespace Prefix:	colb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13,16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_OtherBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Stated interest rate of the subordinated debt.

+ References

No definition available.

+ Details

Name:	us-gaap_SubordinatedBorrowingInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SubordinatedBorrowingLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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- Details

Name:	us-gaap_BusinessAcquisitionAxis=colb_IntermountainCommunityBancorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Other Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
Other Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2014	Nov. 01, 2014
Subordinated Borrowing [Line Items]
Repayments of subordinated debt, Intermountain Statutory Trust I		$ 8.3
Other borrowings		$ 8.2
Subordinated Borrowing, Interest Rate	3.03%
Intermountain Community Bancorp [Member]
Subordinated Borrowing [Line Items]
Business Combination, Purchase Price Allocation, Junior Subordinated Debentures			$ 16.5