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

Interest rate on the amount to be repaid to the counterparty to the sweep product repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

No definition available.

Name:	colb_AssetsSoldunderAgreementstoRepurchaseSweepInterestrate
Namespace Prefix:	colb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Carrying amount of assets sold under term agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets.

No definition available.

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

Interest rate on the amount to be repaid to the counterparty to the Term repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

No definition available.

Name:	colb_AssetsSoldunderAgreementstoRepurchaseTermInterestrate
Namespace Prefix:	colb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729