Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Feb. 29, 2024	Jun. 30, 2023
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2023
Entity File Number	001-34403
Entity Registrant Name	Territorial Bancorp Inc.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	26-4674701
Entity Address, Address Line One	1003 Bishop Street, Pauahi Tower Suite 500
Entity Address, City or Town	Honolulu
Entity Address, State or Province	HI
Entity Address, Postal Zip Code	96813
City Area Code	808
Local Phone Number	946-1400
Title of 12(b) Security	Common stock
Trading Symbol	TBNK
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Public Float			$ 99.2
Entity Filer Category	Non-accelerated Filer
Document Financial Statement Error Correction [Flag]	false
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		8,826,613
Auditor Name	Moss Adams LLP
Auditor Firm ID	659
Auditor Location	Portland, Oregon
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Central Index Key	0001447051
Amendment Flag	false