v2.4.0.6

Covered Assets and FDIC Loss-sharing Asset (Analysis and Allowance for Losses on Covered Loans) (Details) (USD $) In Thousands, unless otherwise specified						12 Months Ended				12 Months Ended						12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Covered Loans [Member]	Dec. 31, 2010 Covered Loans [Member]	Dec. 31, 2009 Covered Loans [Member]	Dec. 31, 2011 Covered Loans [Member] Commercial Portfolio Segment [Member] risk_rating	Dec. 31, 2010 Covered Loans [Member] Commercial Portfolio Segment [Member] risk_rating	Dec. 31, 2011 Covered Loans [Member] Real Estate Portfolio Segment [Member]	Dec. 31, 2010 Covered Loans [Member] Real Estate Portfolio Segment [Member]	Dec. 31, 2011 Covered Loans [Member] Real Estate Portfolio Segment [Member] One-to-Four Family Residential [Member] risk_rating	Dec. 31, 2010 Covered Loans [Member] Real Estate Portfolio Segment [Member] One-to-Four Family Residential [Member] risk_rating	Dec. 31, 2011 Covered Loans [Member] Real Estate Portfolio Segment [Member] Commercial and Multifamily Residential [Member] risk_rating	Dec. 31, 2010 Covered Loans [Member] Real Estate Portfolio Segment [Member] Commercial and Multifamily Residential [Member] risk_rating	Dec. 31, 2011 Covered Loans [Member] Real Estate Construction Portfolio Segment [Member]	Dec. 31, 2010 Covered Loans [Member] Real Estate Construction Portfolio Segment [Member]	Dec. 31, 2011 Covered Loans [Member] Real Estate Construction Portfolio Segment [Member] One-to-Four Family Residential [Member] risk_rating	Dec. 31, 2010 Covered Loans [Member] Real Estate Construction Portfolio Segment [Member] One-to-Four Family Residential [Member] risk_rating	Dec. 31, 2011 Covered Loans [Member] Real Estate Construction Portfolio Segment [Member] Commercial and Multifamily Residential [Member] risk_rating	Dec. 31, 2010 Covered Loans [Member] Real Estate Construction Portfolio Segment [Member] Commercial and Multifamily Residential [Member] risk_rating	Dec. 31, 2011 Covered Loans [Member] Consumer Portfolio Segment [Member] risk_rating	Dec. 31, 2010 Covered Loans [Member] Consumer Portfolio Segment [Member] risk_rating
Covered Assets And FDIC Loss Sharing Asset [Line Items]
Covered Loans			$ 721,313	$ 714,733		$ 195,737	$ 165,255	$ 390,636	$ 409,763	$ 79,328	$ 68,700	$ 311,308	$ 341,063	$ 78,063	$ 81,378	$ 54,402	$ 39,754	$ 23,661	$ 41,624	$ 56,877	$ 58,337
Weighted-Average Risk Rating						6.05	5.74			5.32	4.77	5.65	5.70			7.32	7.29	7.32	6.79	4.84	4.49
Allowance for losses			4,944	6,055	0	977	2,903	3,361	1,834	678	1,013	2,683	821	222	567	136	98	86	469	384	751
Valuation discount resulting from acquisition accounting			184,440	191,617
Loans, net	$ 2,827,259	$ 2,371,822	$ 531,929	$ 517,061

X

- Definition

Acquisition Accounting Valuation Discount on Covered Loans

+ References

No definition available.

+ Details

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

X

- Details

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

X

- Definition

Weighted Average Risk Rating

+ References

No definition available.

+ Details

Name:	colb_WeightedAverageRiskRating
Namespace Prefix:	colb_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The allowance for loan and lease losses represents the reserve to cover probable credit losses related to specifically identified loans and leases, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date. For banks, include currently required allocated transfer risk reserves. Include carryover of or adjustments to the allowance for loan losses in connection with business combinations determined to be appropriate.

+ References

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

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Chapter V

-Section 563c.102

-Paragraph 8

-Subparagraph a(ii)

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.



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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1



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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 114

-Paragraph 20

-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 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 9

-Section 03

-Paragraph 7

-Subparagraph d



Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 8, 9

-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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

X

- Definition

Reflects the aggregate gross carrying amount of all categories of loans and leases held in portfolio, prior to deducting deferred income and the allowance for losses on loans and leases.

+ References

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Reflects the aggregate carrying amount of all categories of loans and leases held in portfolio, net of unearned income and the allowance for losses on loans and leases.

+ References

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetReportedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant