Cover Page - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2023

Feb. 23, 2024

Jun. 30, 2023

Cover [Abstract]

Document Type

10-K

Document Annual Report

true

Document Period End Date

Dec. 31, 2023

Current Fiscal Year End Date

--12-31

Document Transition Report

false

Entity File Number

001-38456

Entity Registrant Name

COLUMBIA FINANCIAL, INC.

Entity Incorporation, State or Country Code

DE

Entity Tax Identification Number

22-3504946

Entity Address, Address Line One

19-01 Route 208 North,

Entity Address, City or Town

Fair Lawn,

Entity Address, State or Province

NJ

Entity Address, Postal Zip Code

07410

City Area Code

800

Local Phone Number

522-4167

Title of 12(b) Security

Common stock, par value $0.01 per share

Trading Symbol

CLBK

Security Exchange Name

NASDAQ

Entity Well-known Seasoned Filer

Yes

Entity Voluntary Filers

No

Entity Current Reporting Status

Yes

Entity Interactive Data Current

Yes

Entity Filer Category

Accelerated Filer

Entity Small Business

false

Entity Emerging Growth Company

false

ICFR Auditor Attestation Flag

true

Document Financial Statement Error Correction [Flag]

false

Entity Shell Company

false

Entity Public Float

$ 429.2

Entity Common Stock, Shares Outstanding (in shares)

104,921,729

Documents Incorporated by Reference

Portions of the Registrant’s Proxy Statement for the 2024 Annual Meeting of Stockholders are incorporated by reference into Part III of this Form 10-K.

Entity Central Index Key

0001723596

Document Fiscal Year Focus

2023

Document Fiscal Period (Q1,Q2,Q3,FY)

FY

Amendment Flag

false