XML 74 R59.htm IDEA: XBRL DOCUMENT
v3.25.3

Loans Receivable, Net - Additional Information (Detail) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2025 USD ($) | Jun. 30, 2025 USD ($) | Mar. 31, 2025 USD ($) | Sep. 30, 2024 USD ($) | Jun. 30, 2024 USD ($) | Mar. 31, 2024 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2025 USD ($) loan | Sep. 30, 2025 USD ($) security_loan | Sep. 30, 2025 USD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2024 USD ($) loan | Dec. 31, 2024 USD ($) security_loan | Dec. 31, 2023 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted-average risk rating | 3.0 |  |  |  |  |  | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 |
Net increase (decrease) in CECL reserve | $ (45,100) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount charged off | 42,111 | $ 45,057 | $ 41,824 | $ 16,989 | $ 12,537 | $ 61,013 |  | $ 128,992 |  |  |  | $ 384,603 |  |  |
CECL reserve | 695,719 | 740,851 | 741,541 | 1,011,059 | 893,938 | 751,370 | $ 695,719 | 695,719 | $ 695,719 | $ 695,719 | $ 695,719 | 733,936 | $ 733,936 | $ 733,936 | $ 576,936
Number of loans |  |  |  |  |  |  |  |  | 137 | 137 |  |  | 130 | 130 |
Principal balance | 18,066,919 |  |  |  |  |  | 18,066,919 | 18,066,919 | $ 18,066,919 | $ 18,066,919 | 18,066,919 | 19,047,518 | $ 19,047,518 | $ 19,047,518 |
Net book value | 17,371,200 |  |  |  |  |  | 17,371,200 | 17,371,200 | $ 17,371,200 | 17,371,200 | 17,371,200 | 18,313,582 | 18,313,582 | 18,313,582 |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 10 |  |  |  |  |  |
Real estate owned, net | 933,635 |  |  |  |  |  | 933,635 | 933,635 | $ 933,635 | 933,635 | 933,635 | 588,185 | 588,185 | 588,185 |
Joint Venture |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan exposure | 43,300 |  |  |  |  |  | 43,300 | 43,300 | 43,300 | 43,300 | 43,300 | 43,300 | 43,300 | 43,300 |
Real estate owned, net | 32,100 |  |  |  |  |  | 32,100 | 32,100 | $ 32,100 | 32,100 | 32,100 | 32,400 | $ 32,400 | 32,400 |
5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 12 |  |  |  | 13 |  |
Principal balance | 1,174,152 |  |  |  |  |  | 1,174,152 | 1,174,152 | $ 1,174,152 | 1,174,152 | 1,174,152 | 1,827,561 | $ 1,827,561 | 1,827,561 |
4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 17 |  |  |  | 20 |  |
Principal balance | 2,732,203 |  |  |  |  |  | 2,732,203 | 2,732,203 | $ 2,732,203 | 2,732,203 | 2,732,203 | 2,707,104 | $ 2,707,104 | 2,707,104 |
3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 80 |  |  |  | 65 |  |
Principal balance | 10,578,120 |  |  |  |  |  | 10,578,120 | 10,578,120 | $ 10,578,120 | 10,578,120 | 10,578,120 | 9,246,692 | $ 9,246,692 | 9,246,692 |
2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 22 |  |  |  | 21 |  |
Principal balance | 3,173,245 |  |  |  |  |  | $ 3,173,245 | 3,173,245 | $ 3,173,245 | 3,173,245 | $ 3,173,245 | 3,346,881 | $ 3,346,881 | 3,346,881 |
Payment Deferral |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |
Aggregate amortized cost basis of loans |  |  |  |  |  |  |  | 367,300 |  |  |  |  |  |  |
Percentage to aggregate loans receivable portfolio |  |  |  |  |  |  |  |  |  |  | 2.00% |  |  |  |
Extended Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |
Aggregate amortized cost basis of loans |  |  |  |  |  |  |  | 506,500 |  |  |  |  |  |  |
Percentage to aggregate loans receivable portfolio |  |  |  |  |  |  |  |  |  |  | 2.80% |  |  |  |
Extended Maturity | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |
Extended Maturity, Loan One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
Proceeds from repayment of loan |  |  |  |  |  |  |  | 6,000 |  |  |  |  |  |  |
Extended Maturity, Loan Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  | 3 years 9 months 18 days |  |  |  |  |  |  |  |
Proceeds from repayment of loan |  |  |  |  |  |  |  | 1,700 |  |  |  |  |  |  |
Extended Maturity, Loan Three |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  | 4 years 9 months 18 days |  |  |  |  |  |  |  |
Increase (decrease) in rate |  |  |  |  |  |  |  |  |  |  | (0.10%) |  |  |  |
Extended Maturity, Loan Four |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |
Increase (decrease) in rate |  |  |  |  |  |  |  |  |  |  | (2.43%) |  |  |  |
Proceeds from repayment of loan |  |  |  |  |  |  |  | 25,000 |  |  |  |  |  |  |
Extended Maturity, Loan Five |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  | 4 years 3 months 18 days |  |  |  |  |  |  |  |
Increase (decrease) in rate |  |  |  |  |  |  |  |  |  |  | (3.56%) |  |  |  |
Extended Maturity, Senior Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |
Extended Maturity, Senior Loans | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |
Extended Maturity, Senior Loans | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
Extended Maturity, Senior Loans | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |
Office |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 42 |  |  |  | 41 |  |
Principal balance | 5,489,331 |  |  |  |  |  | $ 5,489,331 | 5,489,331 | $ 5,489,331 | 5,489,331 | $ 5,489,331 | 7,386,333 | $ 7,386,333 | 7,386,333 |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |
Hospitality |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 14 |  |  |  | 16 |  |
Principal balance | 2,096,519 |  |  |  |  |  | 2,096,519 | 2,096,519 | $ 2,096,519 | 2,096,519 | 2,096,519 | 2,768,374 | $ 2,768,374 | 2,768,374 |
Mixed Use Asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan modifications | loan |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
12 Loans | Impaired loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 12 |  |  |  |  |  |
Cash proceeds | 9,700 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impaired loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount charged off | 42,111 | 45,057 | 41,824 | 16,989 | 12,537 | 61,013 |  |  |  |  |  |  |  |  |
CECL reserve | 505,406 | $ 558,767 | $ 555,379 | $ 883,577 | $ 759,380 | $ 602,599 | 505,406 | 505,406 | $ 505,406 | 505,406 | 505,406 | 580,651 | 580,651 | 580,651 | $ 417,670
Principal balance | 1,174,152 |  |  |  |  |  | 1,174,152 | 1,174,152 | 1,174,152 | 1,174,152 | 1,174,152 | 1,827,561 | 1,827,561 | 1,827,561 |
Impaired loans | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal balance | 1,174,152 |  |  |  |  |  | 1,174,152 | 1,174,152 | 1,174,152 | 1,174,152 | 1,174,152 | 1,827,561 | 1,827,561 | 1,827,561 |
Impaired loans | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal balance | 0 |  |  |  |  |  | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Impaired loans | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal balance | 0 |  |  |  |  |  | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Impaired loans | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal balance | 0 |  |  |  |  |  | 0 | 0 | 0 | 0 | 0 | $ 0 | $ 0 | $ 0 |
Impaired loans | Office |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
CECL reserve | 382,200 |  |  |  |  |  | 382,200 | 382,200 | $ 382,200 | 382,200 | 382,200 |  |  |  |
Unfunded Loan Commitment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loans | loan |  |  |  |  |  |  |  |  | 57 |  |  |  |  |  |
Unfunded Loan Commitment | Payment Deferral |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unfunded loan commitments | 4,700 |  |  |  |  |  | 4,700 | 4,700 | $ 4,700 | 4,700 | 4,700 |  |  |  |
Unfunded Loan Commitment | Extended Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unfunded loan commitments | 32,700 |  |  |  |  |  | $ 32,700 | $ 32,700 | $ 32,700 | $ 32,700 | $ 32,700 |  |  |  |
Asset-specific CECL Reserves |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
(Decrease) increase in net CECL reserve | (53,400) |  |  |  |  |  |  |  |  |  |  |  |  |  |
General CECL Reserves |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
(Decrease) increase in net CECL reserve | $ 8,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition Financing Receivable, Excluding Accrued Interest, Allowance For Credit Loss, Period Increase (Decrease), Net + References No definition available. + Details
Name: | bxmt_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossPeriodIncreaseDecreaseNet
Namespace Prefix: | bxmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Financing Receivable, Excluding Accrued Interest, Before Allowance For Credit Loss, Loan Exposure + References No definition available. + Details
Name: | bxmt_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossLoanExposure
Namespace Prefix: | bxmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Financing Receivable, Excluding Accrued Interest, Period Increase (Decrease) And Writeoff, Net + References No definition available. + Details
Name: | bxmt_FinancingReceivableExcludingAccruedInterestPeriodIncreaseDecreaseAndWriteoffNet
Namespace Prefix: | bxmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Financing Receivable, Modified, Interest Rate Increase (Decrease) From Modification + References No definition available. + Details
Name: | bxmt_FinancingReceivableModifiedInterestRateIncreaseDecreaseFromModification
Namespace Prefix: | bxmt_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivable, Modified, Number Of Contracts + References No definition available. + Details
Name: | bxmt_FinancingReceivableModifiedNumberOfContracts
Namespace Prefix: | bxmt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivable, Modified, Off Balance Sheet Liability + References No definition available. + Details
Name: | bxmt_FinancingReceivableModifiedOffBalanceSheetLiability
Namespace Prefix: | bxmt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Financing Receivable, Number Of Loans + References No definition available. + Details
Name: | bxmt_FinancingReceivableNumberOfLoans
Namespace Prefix: | bxmt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivable, Weighted Average Risk Rating + References No definition available. + Details
Name: | bxmt_FinancingReceivableWeightedAverageRiskRating
Namespace Prefix: | bxmt_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- 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
Name: | us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- Definition Amortized cost excluding accrued interest, after allowance for credit loss, of 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_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-13 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of 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 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-5 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-42 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage, excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty to total financing receivables. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-42 + Details
Name: | us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 12A -Publisher FASB -URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A + Details
Name: | us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The cash inflow associated with the collection, including prepayments, of loans receivable issued for financing of goods and services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-12 + Details
Name: | us-gaap_ProceedsFromCollectionOfLoansReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash inflow from repayments of the balance excluding interest (principal) on loans receivable and leases held for investment purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-12 + Details
Name: | us-gaap_ProceedsFromPrincipalRepaymentsOnLoansAndLeasesHeldForInvestment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement. + 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/2009/role/commonPracticeRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481990/310-10-45-3 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-11 + Details
Name: | us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_CorporateJointVentureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=bxmt_RiskRatingFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=bxmt_RiskRatingFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=bxmt_RiskRatingThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=bxmt_RiskRatingTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=bxmt_ExtendedMaturityLoanOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=bxmt_ExtendedMaturityLoanTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=bxmt_ExtendedMaturityLoanThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=bxmt_ExtendedMaturityLoanFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=bxmt_ExtendedMaturityLoanFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=bxmt_ExtendedMaturitySeniorLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_OfficeBuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=bxmt_HospitalityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=bxmt_MixedUseAssetMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | bxmt_NumberOfLoansAxis=bxmt_A12LoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=bxmt_ImpairedLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bxmt_ImpairedLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_UnfundedLoanCommitmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bxmt_AssetSpecificCECLReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bxmt_GeneralCECLReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |