Financing Receivable, Before Allowance For Credit Loss, Unpaid Principal Balance

No definition available.

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

- Definition

Number of loans held-for-investment as of period-end.

+ References

No definition available.

+ Details

Name:	gpmt_NumberOfLoansHeldForInvestment
Namespace Prefix:	gpmt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Reflects the cumulative amount of unamortized costs incurred to originate loans held-for-investment that are deferred and are being amortized into income as an adjustment to yield.

+ References

No definition available.

+ Details

Name:	gpmt_UnamortizedNetDeferredOriginationFeesLoansHeldforInvestment
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of unfunded commitments for which the entity is obligated, to loans held-for-investment.

+ References

No definition available.

+ Details

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

- Definition

Weighted average coupon rate of all loans held-for-investment as of period-end.

+ References

No definition available.

+ Details

Name:	gpmt_WeightedAverageCouponRateLoansHeldforInvestment
Namespace Prefix:	gpmt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average years to maturity of all loans held-for-investment as of period-end.

+ References

No definition available.

+ Details

Name:	gpmt_WeightedAverageYearsToMaturityLoansHeldForInvestment
Namespace Prefix:	gpmt_
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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

+ Details

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

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, after allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

+ Details

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

- Definition

Amount of realized gain (loss) on investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

+ Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_FirstMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_JuniorLoansMember
Namespace Prefix:
Data Type:	na
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Period Type:

Loans Held-for-Investment, Net of Allowance for Credit Losses - Schedule of Loans Held-for-Investment (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026 USD ($) loan	Mar. 31, 2025 USD ($)	Dec. 31, 2025 USD ($) loan	Dec. 31, 2024 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	$ 1,514,892		$ 1,689,967
Unamortized net deferred origination fees			(6,323)
Allowance for credit losses	(147,298)	$ (177,282)	(145,912)	$ (199,727)
Loans held-for-investment, net	$ 1,362,799	1,760,377	1,537,732	$ 1,897,648
Unfunded commitments			$ 77,399
Number of loans \| loan	40		43
Weighted average coupon (as a percent)			6.20%
Weighted average years to maturity (in years)			6 months
Realized loss on loan sales	$ (18)	$ 0
Senior Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	1,514,892		$ 1,677,017
Unamortized net deferred origination fees	(4,795)		(6,323)
Allowance for credit losses	(147,298)		(145,891)
Loans held-for-investment, net	1,362,799		1,524,803
Unfunded commitments	$ 68,005		$ 77,399
Number of loans \| loan	40		42
Weighted average coupon (as a percent)	5.60%		6.20%
Weighted average years to maturity (in years)	6 months		6 months
B-Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance			$ 12,950
Unamortized net deferred origination fees			0
Allowance for credit losses			(21)
Loans held-for-investment, net			12,929
Unfunded commitments			$ 0
Number of loans \| loan			1
Weighted average coupon (as a percent)			8.00%
Weighted average years to maturity (in years)			1 year 1 month 6 days