Transactions With Related Parties - Our Manager (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Accrued management and incentive fees payable	$ 18,500	$ 26,300
Non-cash compensation expense	$ 31,828	$ 30,655	$ 33,414
Common stock, shares outstanding (in shares)	172,792,094	173,209,933
Restricted Class A Common Stock
Related Party Transaction [Line Items]
Number of shares of restricted class A common stock outstanding (in shares)	2,142,759	2,180,181	1,883,784
Restricted shares, vesting period (in years)	3 years
Related Party
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares)	13,136,754
Percentage of stock	7.60%
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)	412,096
BXMT Advisors Limited Liability Company and Affiliates | Related Party
Related Party Transaction [Line Items]
Management fee payable	$ 18,500
Accrued management and incentive fees payable		$ 26,300
Manager | Related Party
Related Party Transaction [Line Items]
Renewal term (in years)	1 year
Management fees paid to manager	$ 82,600	126,600	$ 104,800
Expenses	$ 1,600	3,400	896
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)	1,320,898
Aggregate grant fair value	$ 28,000
Restricted shares, vesting period (in years)	3 years
Non-cash compensation expense	$ 16,600	$ 14,600	$ 16,600