Fair Value - Nonrecurring Basis (Details) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Valuation Technique [Extensible List]	us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Fair Value, Measurements, Nonrecurring
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Mortgage servicing assets, Fair value	$ 510	$ 452
Mortgage servicing assets, Total losses	(27)	(16)
Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Mortgage servicing assets, Fair value	$ 510	$ 452
Discount rate \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	10.25	10.25
Prepayment speed (CPR) \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	(13.38)	(12.58)
Annual cost to service (per loan, in dollars) \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	75	75
Discounted cash flow model \| Fair Value, Measurements, Nonrecurring \| Level 3 \| Mortgage Servicing Assets
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Fair value	$ 510	$ 452
Minimum \| Discount rate \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	9.25	9.25
Minimum \| Prepayment speed (CPR) \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	9.39	11.09
Maximum \| Discount rate \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	11.25	11.25
Maximum \| Prepayment speed (CPR) \| Fair Value, Measurements, Nonrecurring \| Level 3
Assets Measured at Fair Value on Nonrecurring Basis and Related Losses
Servicing Asset, Measurement Input	17.52	14.24

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

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

- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

+ Details

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

- Definition

The increase (decrease) in the fair value of servicing assets that are subsequently measured at fair value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

+ Details

Name:	us-gaap_ServicingAssetAtFairValuePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of input used to measure servicing asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_ServicingAssetMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Indicates valuation technique for measuring servicing asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_ServicingAssetValuationTechniqueExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	srt-types:extensibleListItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputPrepaymentRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=tbnk_AnnualCostToServiceRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=tbnk_DiscountedCashFlowValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_ServicingContractsMember
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:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: