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Management agreement initial term expiry date.

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Management agreement renewal period.

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Management agreement renewal term description.

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- Definition

percentage of total secured term loans.

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Amount of contractual principal due at origination of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of expense for administrative services provided to the limited liability company (LLC) or limited partnership (LP) by the managing member or general partner, affiliate of managing member or general partner, or affiliate of LLC or LP, for example, but not limited to, salaries, rent, or overhead costs.

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Costs of sales and operating expenses for the period incurred from transactions with related parties.

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Amount of investment in debt security measured at amortized cost (held-to-maturity), investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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Amount paid to managing member or general partner for management of the day-to-day business functions of the limited liability company (LLC) or limited partnership (LP).

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Professional and contract service expense includes cost reimbursements for support services related to contracted projects, outsourced management, technical and staff support.

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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.

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No definition available.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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Amount of noncash expense for share-based payment arrangement.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Transactions with Related Parties - Additional Information (Detail) kr in Billions	3 Months Ended			12 Months Ended
	Mar. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) shares	Mar. 31, 2021 SEK (kr) shares
Related Party Transaction [Line Items]
Non-cash expenses	$ 8,085,000		$ 8,678,000
Loan face amount	$ 17,143,102,000	$ 16,652,824,000		$ 16,652,824,000
Restricted Class A Common Stock [Member]
Related Party Transaction [Line Items]
Management Agreement renewal term, period	1 year
Shares held \| shares	1,707,484	1,627,890		1,627,890	1,707,484
Manager [Member]
Related Party Transaction [Line Items]
Management Agreement expiration date	Dec. 19, 2021
Management Agreement renewal term, description	the current term of which expires on December 19, 2021, and will be automatically renewed for a one-year term upon such date and each anniversary thereafter unless earlier terminated.
Accrued management and incentive fees payable	$ 19,200,000	$ 19,200,000		$ 19,200,000
Management fees paid to Manager	19,200,000			20,200,000
Expenses reimbursed to Manager	$ 40,000			$ 218,000
Manager [Member] \| Class A Common Stock [Member] \| Restricted Class A Common Stock [Member]
Related Party Transaction [Line Items]
Shares held \| shares	856,243				856,243
Non-cash expenses	$ 4,000,000.0
Manager [Member] \| Class A Common Stock [Member] \| Restricted Class A Common Stock [Member] \| Manager [Member]
Related Party Transaction [Line Items]
Non-cash expenses	27,200,000	$ 4,300,000
Affiliates of Manager [Member] \| Third-Party Service Provider [Member]
Related Party Transaction [Line Items]
Administrative services expenses incurred	100,000		133,000
BXMT Advisors Limited Liability Company and Affiliates [Member] \| Twenty Nineteen Term Loan [Member]
Related Party Transaction [Line Items]
Total incentive compensation payments	200,000
Blackstone-Advised Investment Vehicles, or the Funds [Member] \| Senior Loan [Member]
Related Party Transaction [Line Items]
Loan face amount			421,500,000
Blackstone-Advised Investment Vehicles, or the Funds [Member] \| Twenty Nineteen Term Loan [Member]
Related Party Transaction [Line Items]
Debt Securities	$ 5,500,000
percentage of total secured term loans	3.00%				3.00%
Blackstone-Advised Investment Vehicles, or the Funds [Member] \| Senior Term Facility [Member]
Related Party Transaction [Line Items]
Loan face amount \| kr					kr 10.2
Senior term facility			$ 140,000,000.0		kr 5.0
Minority participation in senior term facility	49.00%		33.00%		49.00%