Commitments - Leases (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Reserve Requirements
Federal Reserve Bank reserve requirements	$ 13.5	$ 11.9

Represents the amount of Federal Reserve Bank reserve requirement.

No definition available.

Name:	tbnk_FederalReserveBankReserveRequirementAmount
Namespace Prefix:	tbnk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant