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

Includes amounts charged depositors for: (1) maintenance of their accounts (maintenance charges); (2) failure to maintain specified minimum balances on account; (3) exceeding the number of checks or transactions allowed to be processed in a given period; (4) checks drawn on no minimum balance deposit accounts; (5) withdrawals from nontransaction deposit accounts; (6) closing savings accounts before a specified minimum period of time has elapsed; (7) accounts which have remained inactive for extended periods of time or which have become dormant; (8) use of automated teller machines or remote service units; (9) checks drawn against insufficient funds that the bank assesses regardless of whether it decides to pay, return or hold the check; (10) issuing stop payment orders; (11) certifying checks; and (12) accumulating or disbursing funds deposited in IRAs or Keogh Plan accounts when not handled by the bank's trust department.

No definition available.

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

Gross income from services rendered by the trust subsidiary, acting in any fiduciary capacity. Also include fees and commissions from the financial services department, including securities brokerage activities, investment advisory and management services.

No definition available.

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

Noninterest income, excluding revenue from contracts with customers

No definition available.

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

Revenue from contracts with customers

No definition available.

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

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

The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13)
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260