Parent Company Only - Condensed Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 21,995	$ 19,212
Adjustments to reconcile net income to net cash provided by operating activities:
Net (increase) decrease in prepaid expenses and other assets	81	1,315
Net cash from operating activities	22,327	21,626
Cash flows from investing activities:
Net cash from investing activities	(6,037)	(53,761)
Cash flows from financing activities:
Proceeds from issuance of common stock	170
Repurchases of common stock	(1,597)	(9,270)
Cash dividends paid	(13,689)	(10,490)
Net cash from financing activities	(18,547)	47,109
Net (decrease) increase in cash and cash equivalents	(2,257)	14,974
Cash and cash equivalents at beginning of the period	47,063	32,089
Cash and cash equivalents at end of the period	44,806	47,063
Territorial Bancorp Inc.
Cash flows from operating activities:
Net income	21,995	19,212
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of Territorial Savings Bank, net of dividends	(1,252)	(5,391)
ESOP expense	1,398	1,456
Net (increase) decrease in prepaid expenses and other assets	(715)	785
Net increase (decrease) in other liabilities	(97)	(6)
Net cash from operating activities	21,329	16,056
Cash flows from financing activities:
Proceeds from issuance of common stock	170
Repurchases of common stock	(1,597)	(9,270)
Cash dividends paid	(13,689)	(10,490)
Net cash from financing activities	(15,116)	(19,760)
Net (decrease) increase in cash and cash equivalents	6,213	(3,704)
Cash and cash equivalents at beginning of the period	16,389	20,093
Cash and cash equivalents at end of the period	$ 22,602	$ 16,389