Parent Company Only - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Prepaid expenses and other assets	$ 2,800	$ 2,537
Total assets	2,086,313	2,069,206
Liabilities and Equity
Equity	243,890	235,079	$ 234,854
Total liabilities and stockholders' equity	2,086,313	2,069,206
Territorial Bancorp Inc.
Assets
Cash	22,602	16,389
Investment in Territorial Savings Bank	219,838	217,884
Receivable from Territorial Savings Bank	1,377	741
Prepaid expenses and other assets	233	154
Total assets	244,050	235,168
Liabilities and Equity
Other liabilities	160	89
Equity	243,890	235,079
Total liabilities and stockholders' equity	$ 244,050	$ 235,168