Deposits (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Deposits [Abstract]
Brokered money market accounts	$ 83,402,000colb_BrokeredMoneyMarketAccounts	$ 41,765,000colb_BrokeredMoneyMarketAccounts
Demand and other noninterest-bearing	2,651,373,000	2,171,703,000
Interest-bearing demand	1,304,258,000	1,170,006,000
Money market	1,760,331,000us-gaap_DepositsMoneyMarketDeposits	1,569,261,000us-gaap_DepositsMoneyMarketDeposits
Savings	615,721,000us-gaap_DepositsSavingsDeposits	496,444,000us-gaap_DepositsSavingsDeposits
Certificates of deposit less than $100,000	288,261,000us-gaap_TimeDepositsLessThan100000	288,943,000us-gaap_TimeDepositsLessThan100000
Total core deposits	6,619,944,000colb_CoreDeposits	5,696,357,000colb_CoreDeposits
Certificates of deposit greater than $100,000	202,014,000us-gaap_TimeDeposits100000OrMore	201,498,000us-gaap_TimeDeposits100000OrMore
Certificates of deposit insured by CDARS®	18,429,000	19,488,000
Subtotal	6,923,789,000colb_CoreAndOtherDeposits	5,959,108,000colb_CoreAndOtherDeposits
Deposits, Valuation Adjustment From Acquisition Accounting	933,000	367,000
Total deposits	6,924,722,000us-gaap_Deposits	5,959,475,000us-gaap_Deposits
Deposit Liabilities Reclassified as Loans Receivable	1,300,000	1,100,000
Time Deposits, Fiscal Year Maturity [Abstract]
2015	162,828,000us-gaap_TimeDepositMaturitiesYearOne
2016	40,375,000us-gaap_TimeDepositMaturitiesYearTwo
2017	8,069,000us-gaap_TimeDepositMaturitiesYearThree
2018	3,822,000us-gaap_TimeDepositMaturitiesYearFour
2019	3,982,000us-gaap_TimeDepositMaturitiesYearFive
Thereafter	108,000
Total	$ 219,184,000us-gaap_TimeDeposits

Brokered money market accounts

No definition available.

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- Definition

Certificates Of Deposit Insured By CDARS

+ References

No definition available.

+ Details

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- Definition

Core And Other Deposits

+ References

No definition available.

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- Definition

Core Deposits

+ References

No definition available.

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- Definition

Deposits, Valuation Adjustment From Acquisition Accounting

+ References

No definition available.

+ Details

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- Definition

Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

+ References

+ Details

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- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ 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 210.9-03.12)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 9

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- Definition

Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

+ References

+ Details

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- Definition

Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).

+ References

+ Details

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- Definition

Amount of money in interest-bearing domestic accounts that entitle the depositor to withdraw funds at any time without prior notice, also known as demand deposits.

+ References

+ Details

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- Definition

Amount of domestic noninterest-bearing deposits held by the entity, which may include demand deposits, checking, brokered and retail deposits.

+ References

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- Definition

Amount of time deposits maturing after the fifth fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of time deposits maturing in the fifth fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of time deposits maturing in the fourth fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of time deposits maturing in the next fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of time deposits maturing in the third fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of time deposits maturing in the second fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of deposits that cannot be withdrawn before a set date without penalty or for which notice of withdrawal is required. Time deposits include, but are not limited to, certificates of deposits, individual retirement accounts and open accounts.

+ References

+ Details

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- Definition

The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 405

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6479006&loc=d3e64164-112818

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

-Publisher SEC

-Name Industry Guide

-Number 3

-Section V

-Paragraph A

-Subparagraph 4

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- Definition

The aggregate amount of domestic or foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $100,000.

+ References

No definition available.

+ Details

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