Secured Borrowings - Collateralized Loan Obligations (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security	Feb. 28, 2022 USD ($)	Jan. 31, 2022 USD ($)	May 31, 2021 USD ($)	Apr. 30, 2021 USD ($)	Aug. 31, 2019 USD ($)
Summary of CLO
Carrying Value	$ 3,223,867	$ 3,491,292
Collateral assets
Summary of CLO
Face Amount	3,864,515	4,226,614
Carrying Value	4,023,888	4,288,770
Financing
Summary of CLO
Face Amount	3,231,326	3,500,163
Carrying Value	$ 3,223,867	$ 3,491,292
STWD 2022-FL3
Summary of CLO
Face Amount			$ 1,000,000
STWD 2022-FL3 | Collateral assets
Summary of CLO
Count | security	46	48
Face Amount	$ 1,000,000	$ 997,569
Carrying Value	$ 1,007,284	$ 1,007,532
STWD 2022-FL3 | Collateral assets | SOFR
Summary of CLO
Weighted Average Spread	3.49%	3.53%
STWD 2022-FL3 | Financing
Summary of CLO
Count | security	1	1
Face Amount	$ 840,620	$ 840,620
Carrying Value	$ 837,805	$ 837,881
STWD 2022-FL3 | Financing | SOFR
Summary of CLO
Weighted Average Spread	1.89%	1.89%
STWD 2021-HTS | Collateral assets
Summary of CLO
Count | security	1	1
Face Amount	$ 210,181	$ 223,193
Carrying Value	$ 216,750	$ 224,509
STWD 2021-HTS | Collateral assets | SOFR
Summary of CLO
Weighted Average Spread	4.02%	3.87%
STWD 2021-HTS | Financing
Summary of CLO
Count | security	1	1
Face Amount	$ 195,576	$ 203,284
Carrying Value	$ 195,576	$ 203,058
STWD 2021-HTS | Financing | SOFR
Summary of CLO
Weighted Average Spread	2.42%	2.82%
STWD 2021-FL2
Summary of CLO
Face Amount					$ 1,300,000
Percent of outstanding loan	7.00%
Debt, weighted average interest rate	7.39%
STWD 2021-FL2 | Collateral assets
Summary of CLO
Count | security	31	34
Face Amount	$ 1,206,319	$ 1,272,585
Carrying Value	$ 1,216,834	$ 1,288,165
STWD 2021-FL2 | Collateral assets | SOFR
Summary of CLO
Weighted Average Spread	3.81%	3.95%
STWD 2021-FL2 | Financing
Summary of CLO
Count | security	1	1
Face Amount	$ 988,749	$ 1,065,713
Carrying Value	$ 987,167	$ 1,063,454
STWD 2021-FL2 | Financing | SOFR
Summary of CLO
Weighted Average Spread	1.89%	1.85%
STWD 2019-FL1
Summary of CLO
Face Amount							$ 1,100,000
STWD 2019-FL1 | Collateral assets
Summary of CLO
Count | security	10	14
Face Amount	$ 550,006	$ 734,099
Carrying Value	$ 553,096	$ 739,684
STWD 2019-FL1 | Collateral assets | SOFR
Summary of CLO
Weighted Average Spread	3.58%	3.51%
STWD 2019-FL1 | Financing
Summary of CLO
Count | security	1	1
Face Amount	$ 386,381	$ 570,546
Carrying Value	$ 386,380	$ 570,546
STWD 2019-FL1 | Financing | SOFR
Summary of CLO
Weighted Average Spread	1.83%	1.62%
STWD 2021-SIF2
Summary of CLO
Face Amount				$ 500,000
STWD 2021-SIF2 | Collateral assets
Summary of CLO
Count | security	28	30
Face Amount	$ 458,687	$ 499,401
Carrying Value	$ 514,678	$ 514,286
STWD 2021-SIF2 | Collateral assets | SOFR
Summary of CLO
Weighted Average Spread	3.80%	3.87%
STWD 2021-SIF2 | Financing
Summary of CLO
Count | security	1	1
Face Amount	$ 410,000	$ 410,000
Carrying Value	$ 408,393	$ 408,166
STWD 2021-SIF2 | Financing | SOFR
Summary of CLO
Weighted Average Spread	2.11%	2.11%
STWD 2021-SIF1
Summary of CLO
Face Amount						$ 500,000
Percent of outstanding loan	2.00%
Debt, weighted average interest rate	5.68%
STWD 2021-SIF1 | Collateral assets
Summary of CLO
Count | security	30	32
Face Amount	$ 439,322	$ 499,767
Carrying Value	$ 515,246	$ 514,594
STWD 2021-SIF1 | Collateral assets | SOFR
Summary of CLO
Weighted Average Spread	3.88%	3.97%
STWD 2021-SIF1 | Financing
Summary of CLO
Count | security	1	1
Face Amount	$ 410,000	$ 410,000
Carrying Value	$ 408,546	$ 408,187
STWD 2021-SIF1 | Financing | SOFR
Summary of CLO
Weighted Average Spread	2.42%	2.42%