| Cover | Sep. 30, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 30, 2024 |
| Entity Registrant Name | Columbia Banking System, Inc. |
| Entity Incorporation, State or Country Code | WA |
| Entity File Number | 000-20288 |
| Entity Tax Identification Number | 91-1422237 |
| Entity Address, Address Line One | 1301 A Street |
| Entity Address, City or Town | Tacoma |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98402-4200 |
| City Area Code | 253 |
| Local Phone Number | 305-1900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(g) Security | Common Stock |
| Trading Symbol | COLB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000887343 |
| Amendment Flag | false |
