v3.26.1
Fair Value Measurements (Details) - EBP 001 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value $ 836,653 $ 749,453
Common stock – Columbia Banking System, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 15,100 15,200
Total    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 397,557 364,036
Total | Money markets and other cash equivalents    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 176 60
Total | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 379,666 344,389
Total | Common stock – Columbia Banking System, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 15,070 15,200
Total | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 2,645 4,387
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 397,557 364,036
Level 1 | Money markets and other cash equivalents    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 176 60
Level 1 | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 379,666 344,389
Level 1 | Common stock – Columbia Banking System, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 15,070 15,200
Level 1 | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 2,645 4,387
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 2 | Money markets and other cash equivalents    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 2 | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 2 | Common stock – Columbia Banking System, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 2 | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3 | Money markets and other cash equivalents    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3 | Registered investment companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3 | Common stock – Columbia Banking System, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3 | Self-directed brokerage accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
NAV | Collective trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value $ 439,096 $ 385,417