| Cover | May 18, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 18, 2023 |
| Entity File Number | 1-34403 |
| Entity Registrant Name | TERRITORIAL BANCORP INC. |
| Entity Central Index Key | 0001447051 |
| Entity Tax Identification Number | 26-4674701 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | 1003 Bishop Street |
| Entity Address, Address Line Two | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | TBNK |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
