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Summary of Significant Accounting Policies (Details) | 9 Months Ended | 12 Months Ended |  |  |  |  |  |  |
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Sep. 30, 2025 USD ($) real_estate_owned_asset | Sep. 30, 2025 USD ($) loan real_estate_owned_asset | Sep. 30, 2025 USD ($) security_loan real_estate_owned_asset | Dec. 31, 2024 USD ($) loan real_estate_owned_asset | Dec. 31, 2024 USD ($) real_estate_owned_asset security_loan | Jun. 30, 2025 USD ($) | Mar. 31, 2025 USD ($) | Sep. 30, 2024 USD ($) | Jun. 30, 2024 USD ($) | Mar. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Restricted cash | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 |  |  |  |  |  |  |
Number of REO assets classified as held for sale investment | real_estate_owned_asset | 10 | 10 | 10 | 7 | 7 |  |  |  |  |  |  |
Maximum guarantee | $ 5,500,000 | $ 5,500,000 | $ 5,500,000 | $ 5,500,000 | $ 5,500,000 |  |  |  |  |  |  |
Guarantee liability | 32,000 | 32,000 | 32,000 | 32,000 | 32,000 |  |  |  |  |  |  |
CECL reserve | 695,719,000 | $ 695,719,000 | $ 695,719,000 | $ 733,936,000 | $ 733,936,000 | $ 740,851,000 | $ 741,541,000 | $ 1,011,059,000 | $ 893,938,000 | $ 751,370,000 | $ 576,936,000 |
Number of loans |  | 137 | 137 | 130 | 130 |  |  |  |  |  |  |
Principal balance | $ 18,066,919,000 | $ 18,066,919,000 | $ 18,066,919,000 | $ 19,047,518,000 | $ 19,047,518,000 |  |  |  |  |  |  |
Net Lease Joint Venture |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage | 75.00% | 75.00% | 75.00% | 75.00% | 75.00% |  |  |  |  |  |  |
Level 3 | Minimum | Capitalization rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Measurement input | 0.0600 | 0.0600 | 0.0600 |  |  |  |  |  |  |  |  |
Level 3 | Minimum | Discount rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Measurement input | 0.0700 | 0.0700 | 0.0700 |  |  |  |  |  |  |  |  |
Level 3 | Maximum | Capitalization rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Measurement input | 0.0800 | 0.0800 | 0.0800 |  |  |  |  |  |  |  |  |
Level 3 | Maximum | Discount rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Measurement input | 0.1500 | 0.1500 | 0.1500 |  |  |  |  |  |  |  |  |
Level 3 | Fair Value, Nonrecurring |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
CECL reserve | $ 505,400,000 | $ 505,400,000 | $ 505,400,000 |  |  |  |  |  |  |  |  |
Number of loans | loan |  | 12 |  |  |  |  |  |  |  |  |  |
Principal balance | $ 1,200,000,000 | $ 1,200,000,000 | $ 1,200,000,000 |  |  |  |  |  |  |  |  |
Level 3 | Fair Value, Nonrecurring | Minimum | Capitalization rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Real estate owned, measurement input | 0.0600 | 0.0600 | 0.0600 |  |  |  |  |  |  |  |  |
Level 3 | Fair Value, Nonrecurring | Minimum | Discount rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Real estate owned, measurement input | 0.0775 | 0.0775 | 0.0775 |  |  |  |  |  |  |  |  |
Level 3 | Fair Value, Nonrecurring | Maximum | Capitalization rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Real estate owned, measurement input | 0.0855 | 0.0855 | 0.0855 |  |  |  |  |  |  |  |  |
Level 3 | Fair Value, Nonrecurring | Maximum | Discount rate |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Real estate owned, measurement input | 0.1055 | 0.1055 | 0.1055 |  |  |  |  |  |  |  |  |
Building |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful lives (in years) | 40 years |  |  |  |  |  |  |  |  |  |  |
Leasehold Improvements |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful lives (in years) | 10 years |  |  |  |  |  |  |  |  |  |  |
Multifamily Joint Venture |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  |  |  |  | 85.00%
Multifamily Joint Venture | Walker & Dunlop |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Minority participation in senior term facility |  |  |  |  |  |  |  |  |  |  |  | 15.00%

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