Secured Borrowings - Collateralized Loan Obligations (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) security	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 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	$ 3,518,274	$ 3,518,274	$ 3,676,224
Collateral assets
Summary of CLO
Face Amount	4,240,575	4,240,575	4,401,641
Carrying Value	4,303,188	4,303,188	4,454,087
Financing
Summary of CLO
Face Amount	3,527,982	3,527,982	3,689,140
Carrying Value	$ 3,518,274	$ 3,518,274	$ 3,676,224
SOFR
Summary of CLO
Weighted Average Spread	2.53%
STWD 2022-FL3
Summary of CLO
Face Amount				$ 1,000,000
STWD 2022-FL3 | Collateral assets
Summary of CLO
Count | security	50	50	51
Face Amount	$ 999,998	$ 999,998	$ 1,000,000
Carrying Value	$ 1,009,424	$ 1,009,424	$ 1,010,051
STWD 2022-FL3 | Financing
Summary of CLO
Count | security	1	1	1
Face Amount	$ 842,500	$ 842,500	$ 842,500
Carrying Value	$ 840,414	$ 840,414	$ 842,374
STWD 2022-FL3 | SOFR | Collateral assets
Summary of CLO
Weighted Average Spread		3.53%
STWD 2022-FL3 | SOFR | Financing
Summary of CLO
Weighted Average Spread		1.93%	1.93%
STWD 2022-FL3 | Index | Collateral assets
Summary of CLO
Weighted Average Spread			3.52%
STWD 2021-HTS | Collateral assets
Summary of CLO
Count | security	1	1	1
Face Amount	$ 230,000	$ 230,000	$ 230,000
Carrying Value	$ 231,293	$ 231,293	$ 231,186
STWD 2021-HTS | Financing
Summary of CLO
Count | security	1	1	1
Face Amount	$ 210,091	$ 210,091	$ 210,091
Carrying Value	$ 209,639	$ 209,639	$ 208,961
STWD 2021-HTS | SOFR | Collateral assets
Summary of CLO
Weighted Average Spread		3.87%
STWD 2021-HTS | SOFR | Financing
Summary of CLO
Weighted Average Spread		2.75%
STWD 2021-HTS | LIBOR | Collateral assets
Summary of CLO
Weighted Average Spread			3.85%
STWD 2021-HTS | LIBOR | Financing
Summary of CLO
Weighted Average Spread			2.71%
STWD 2021-FL2
Summary of CLO
Face Amount						$ 1,300,000
Percent of outstanding loan	6.00%	6.00%
Debt, weighted average interest rate	7.40%	7.40%
STWD 2021-FL2 | Collateral assets
Summary of CLO
Count | security	36	36	36
Face Amount	$ 1,275,042	$ 1,275,042	$ 1,277,474
Carrying Value	$ 1,288,073	$ 1,288,073	$ 1,284,240
STWD 2021-FL2 | Financing
Summary of CLO
Count | security	1	1	1
Face Amount	$ 1,077,375	$ 1,077,375	$ 1,077,375
Carrying Value	$ 1,074,437	$ 1,074,437	$ 1,072,403
STWD 2021-FL2 | SOFR | Financing
Summary of CLO
Weighted Average Spread		1.85%
STWD 2021-FL2 | Index | Collateral assets
Summary of CLO
Weighted Average Spread		3.94%	4.04%
STWD 2021-FL2 | LIBOR | Financing
Summary of CLO
Weighted Average Spread			1.80%
STWD 2019-FL1
Summary of CLO
Face Amount								$ 1,100,000
STWD 2019-FL1 | Collateral assets
Summary of CLO
Count | security	14	14	16
Face Amount	$ 737,444	$ 737,444	$ 902,799
Carrying Value	$ 747,484	$ 747,484	$ 906,409
STWD 2019-FL1 | Financing
Summary of CLO
Count | security	1	1	1
Face Amount	$ 578,016	$ 578,016	$ 739,174
Carrying Value	$ 578,016	$ 578,016	$ 738,473
STWD 2019-FL1 | SOFR | Financing
Summary of CLO
Weighted Average Spread		1.64%	1.64%
STWD 2019-FL1 | Index | Collateral assets
Summary of CLO
Weighted Average Spread		3.49%	3.67%
STWD 2021-SIF2
Summary of CLO
Face Amount					$ 500,000
STWD 2021-SIF2 | Collateral assets
Summary of CLO
Count | security	30	30	31
Face Amount	$ 498,888	$ 498,888	$ 495,587
Carrying Value	$ 513,296	$ 513,296	$ 510,730
STWD 2021-SIF2 | Financing
Summary of CLO
Count | security	1	1	1
Face Amount	$ 410,000	$ 410,000	$ 410,000
Carrying Value	$ 407,940	$ 407,940	$ 407,260
STWD 2021-SIF2 | SOFR | Collateral assets
Summary of CLO
Weighted Average Spread		3.87%
STWD 2021-SIF2 | SOFR | Financing
Summary of CLO
Weighted Average Spread		2.11%	2.11%
STWD 2021-SIF2 | Index | Collateral assets
Summary of CLO
Weighted Average Spread			3.73%
STWD 2021-SIF1
Summary of CLO
Face Amount							$ 500,000
Percent of outstanding loan	2.00%	2.00%
Debt, weighted average interest rate	5.70%	5.70%
STWD 2021-SIF1 | Collateral assets
Summary of CLO
Count | security	31	31	31
Face Amount	$ 499,203	$ 499,203	$ 495,781
Carrying Value	$ 513,618	$ 513,618	$ 511,471
STWD 2021-SIF1 | Financing
Summary of CLO
Count | security	1	1	1
Face Amount	$ 410,000	$ 410,000	$ 410,000
Carrying Value	$ 407,828	$ 407,828	$ 406,753
STWD 2021-SIF1 | SOFR | Collateral assets
Summary of CLO
Weighted Average Spread		3.98%
STWD 2021-SIF1 | SOFR | Financing
Summary of CLO
Weighted Average Spread		2.22%
STWD 2021-SIF1 | Index | Collateral assets
Summary of CLO
Weighted Average Spread			3.76%
STWD 2021-SIF1 | LIBOR | Financing
Summary of CLO
Weighted Average Spread			2.15%