Real Estate Owned, Net - Schedule of Real Estate Acquired Through Foreclosure Financial Statements, Disclosure (Details) - Discontinued Operations, Held-for-Sale - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Real Estate [Line Items]
Accumulated Depreciation	$ (5,830)	$ (4,707)
Real estate owned, net	93,239	92,039
Intangible real estate assets	18,844	18,909
Accumulated amortization	(6,515)	(5,615)
Intangible real estate assets, net	12,329	13,294
Lease liability	(7,237)	(7,239)
Intangible real estate liabilities	(196)	(195)
Accumulated amortization	74	61
Real estate liabilities, net	(7,359)	(7,373)
Building and Building Improvements
Real Estate [Line Items]
Real estate owned, net	88,675	86,350
Land and Land Improvements
Real Estate [Line Items]
Real estate owned, net	$ 10,394	$ 10,396

Disposal Group, Including Discontinued Operation, Accumulated Depreciation

No definition available.

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationAccumulatedDepreciation
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Disposal Group, Including Discontinued Operation, Accumulated Depreciation Liabilities

+ References

No definition available.

+ Details

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationAccumulatedDepreciationLiabilities
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Disposal Group, Including Discontinued Operation, Intangible Assets , Accumulated Depreciation

+ References

No definition available.

+ Details

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationIntangibleAssetsAccumulatedDepreciation
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Disposal Group Including Discontinued Operation Intangible Assets, Net

+ References

No definition available.

+ Details

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationIntangibleAssetsNet
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Disposal Group, Including Discontinued Operation, Intangible Real Estate Liabilities

+ References

No definition available.

+ Details

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationIntangibleRealEstateLiabilities
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Disposal Group, Including Discontinued Operation, Lease Liability

+ References

No definition available.

+ Details

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationLeaseLiability
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Disposal Group, Including Discontinued Operation, Property, Plant And Equipment, Net

+ References

No definition available.

+ Details

Name:	gpmt_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentNet
Namespace Prefix:	gpmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount classified as intangible assets, excluding goodwill, attributable to disposal group held for sale or disposed of.

+ References

+ Details

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

- Definition

Amount classified as property, plant and equipment attributable to disposal group held for sale or disposed of.

+ References

+ Details

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

- Definition

Amount classified as liabilities attributable to disposal group held for sale or disposed of.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 10
-SubTopic 20
-Topic 205
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483475/205-20-45-10

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-7

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5C
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-5C

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-5B

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-3

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483475/205-20-45-11

+ Details

Name:	us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 976
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477332/976-310-50-1

+ Details

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

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsHeldforsaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingAndBuildingImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LandAndLandImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: