Loans Receivable and Allowance for Loan Losses - Delinquent and Nonaccrual Loans (Details)	12 Months Ended
Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Accounts, Notes, Loans and Financing Receivable
Nonaccrual Loans	$ 736,000	$ 2,213,000
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable
Number of loans \| loan	1	0
Fixed-rate mortgage loans \| Minimum
Accounts, Notes, Loans and Financing Receivable
Loan delinquency period that may result in loss	90 days
Loan delinquency period after which an appraisal is obtained of the underlying collateral	4 months
Non Accrual Loans
Accounts, Notes, Loans and Financing Receivable
Number of loans \| loan	6	11
Nonaccrual Loans	$ 736,000	$ 2,200,000
Interest collected on nonaccrual loans recorded as a reduction of principal	58,000	93,000
Non accrual loans, additional interest income that would have been recognized had the loans been accruing interest	$ 60,000	$ 133,000

Reflects the amount of interest collected on impaired or nonperforming loans recorded as a reduction of principal.

No definition available.

Name:	tbnk_LoansAndLeasesReceivableImpairedInterestCollectedOnNonaccrualLoansRecordedAsReductionOfPrincipal
Namespace Prefix:	tbnk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the number of mortgage loans outstanding.

+ References

No definition available.

+ Details

Name:	tbnk_NumberOfMortgageLoans
Namespace Prefix:	tbnk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Threshold period past due for obtaining appraisal of underlying collateral to financing receivable, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	tbnk_ThresholdPeriodPastDueForObtainingAppraisalForCollateralToFinancingReceivable
Namespace Prefix:	tbnk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Threshold period for when financing receivable is considered past due to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919253-210447

+ Details

Name:	us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=tbnk_NonAccrualLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: