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Real estate estimated fair value determined by third-party appraisal.

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- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=cmtg_RealEstateOwnedHeld-For-SaleMember
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Real Estate Owned - Additional Information (Details)	1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended
Real Estate Owned - Additional Information (Details)	Oct. 31, 2026 USD ($) Hotel	Sep. 30, 2026 USD ($)	May 31, 2026 USD ($)	Jan. 31, 2026 USD ($)	Sep. 30, 2026 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2026 USD ($)	Sep. 30, 2025 USD ($)	Dec. 31, 2025 USD ($)
Mortgage Loans On Real Estate [Line Items]
Real Estate Owned Held-For-Sale		$ 53,141,000			$ 53,141,000		$ 53,141,000
Restricted cash		15,558,000			15,558,000	$ 16,743,000	15,558,000	$ 16,743,000	$ 17,599,000
Other assets		113,941,000			113,941,000		113,941,000		143,372,000
Other liabilities		24,888,000			24,888,000		24,888,000		37,063,000
Real estate estimated fair value							59,800,000
Depreciation expense					4,100,000	$ 2,000,000	$ 12,800,000	2,600,000
Weighted average amortization period for in-place lease values							1 year
Impairment of real estate							$ 0
Gain (loss) on sales of real estate owned							341,000	$ 366,000
Unpaid Principal Balance Before Principal Charge-Off / Valuation Allowance									71,300,000
Multifamily Properties
Mortgage Loans On Real Estate [Line Items]
Principal charge-off				$ 76,600,000			$ 800,000		39,100,000
Fair value discount rate							8.00%
Transaction costs							$ 300,000
Multifamily Properties \| Minimum
Mortgage Loans On Real Estate [Line Items]
Fair value market capitalization rate							5.00%
Multifamily Properties \| Maximum
Mortgage Loans On Real Estate [Line Items]
Fair value market capitalization rate							5.75%
Multifamily Properties \| TX
Mortgage Loans On Real Estate [Line Items]
Principal charge-off			$ 2,700,000
Real estate estimated fair value			22,400,000						$ 37,400,000
Transaction costs			200,000
Sale price		22,500,000	48,000,000
Property's carrying value		22,100,000	46,700,000		22,100,000		$ 22,100,000
Gain (loss) on sales of real estate owned			300,000
Unpaid Principal Balance Before Principal Charge-Off / Valuation Allowance			25,400,000
Accrued interest receivable			$ 400,000
Hotel \| Subsequent Event
Mortgage Loans On Real Estate [Line Items]
Number of hotels sold \| Hotel	2
Number of hotels held in portfolio \| Hotel	7
Sale price	$ 44,500,000
Real Estate Owned Held-For-Sale
Mortgage Loans On Real Estate [Line Items]
Loss from our valuation adjustment for real estate owned held-for-sale		$ 27,800,000			$ 27,800,000		$ 27,800,000