Transactions With Related Parties - Our Manager (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Related Party Transaction [Line Items]
Accrued management and incentive fees payable	$ 17,200		$ 18,500
Non-cash compensation expense	$ 6,965	$ 8,112
Common stock, shares outstanding (in shares)	171,582,452		172,792,094
Restricted Class A Common Stock
Related Party Transaction [Line Items]
Number of shares of restricted class A common stock outstanding (in shares)	2,395,727		2,142,759
Restricted shares, vesting period (in years)	3 years
Related Party
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares)	13,593,458
Percentage of stock	7.90%
Subsidiary of Common Parent
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares)	8,234,581
Percentage of stock	4.80%
Director | Deferred Stock Units
Related Party Transaction [Line Items]
Number of shares of restricted class A common stock outstanding (in shares)	310,108
BXMT Advisors Limited Liability Company and Affiliates | Related Party
Related Party Transaction [Line Items]
Management fee payable	$ 17,200		$ 18,500
Manager | Related Party
Related Party Transaction [Line Items]
Renewal term (in years)	1 year
Management fees paid to manager	$ 18,500	26,300
Expenses	$ 264	221
Manager | Related Party | Restricted Class A Common Stock
Related Party Transaction [Line Items]
Number of shares of restricted class A common stock outstanding (in shares)	1,211,048
Aggregate grant fair value	$ 25,400
Restricted shares, vesting period (in years)	3 years
Non-cash compensation expense	$ 3,600	$ 4,300