Stockholders' Equity and Non-Controlling Interests - Narrative (Details) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 06, 2021 USD ($)	Nov. 05, 2021 USD ($)	Apr. 30, 2022 USD ($) shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) extension $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Dec. 31, 2022 USD ($)	Dec. 31, 2018 shares	May 31, 2022 USD ($)
Equity Incentive Plans
Commission costs under ATM agreement						$ 0	$ 756
Contributions from non-controlling interests						0	21,926
Net income				$ 3,114	$ 23,795	51,062	134,298
Net income (loss) attributable to non-controlling interests				$ 3,942	29,276	$ 65,265	158,409
CMBS JV
Equity Incentive Plans
Participation / Ownership %				51.00%		51.00%
Class A Units
Equity Incentive Plans
Number of units outstanding (in shares) | shares				9,800,000		9,800,000
Woodstar II Portfolio | Class A Units
Equity Incentive Plans
Net income (loss) attributable to non-controlling interests				$ 4,700	4,700	$ 14,100	14,100
Subsidiaries | Woodstar II Portfolio
Equity Incentive Plans
Conversion of stock ratio						1
Subsidiaries | Woodstar II Portfolio | Class A Units
Equity Incentive Plans
Shares issued (in shares) | shares									10,200,000
Right to receive additional shares (in shares) | shares						1,900,000			1,900,000
Subsidiaries | Woodstar II Portfolio | Class A Units | Non- Controlling Interests
Equity Incentive Plans
Redemption of units						$ 208,500		$ 208,500
Woodstar Fund
Equity Incentive Plans
Percentage of interest sold		20.60%
Contributions from non-controlling interests	$ 214,200	$ 216,000
Initial term						8 years
Number of extension options | extension						2
Extension term						1 year
CMBS JV
Equity Incentive Plans
Non-controlling interest				$ 135,600		$ 135,600		$ 144,300
CMBS JV | Joint Venture Partner
Equity Incentive Plans
Ownership percentage				49.00%		49.00%
CMBS JV | Woodstar II Portfolio | Class A Units
Equity Incentive Plans
Net income (loss) attributable to non-controlling interests				$ (4,500)	$ (400)	$ (1,600)	$ 4,500
Starwood Property Trust, Inc. Equity Plan and Manager Equity Plan
Equity Incentive Plans
Number of shares of authorized for issuance (in shares) | shares			18,700,000
Common stock available for future grants (in shares) | shares				16,500,000		16,500,000
Employee Stock
Equity Incentive Plans
Purchase price of fair market value (as a percent)			85.00%
Maximum purchase value during calendar year, per employee			$ 25
Number of shares of authorized for issuance (in shares) | shares			2,000,000
Number of shares issued for future grants (in shares) | shares				21,088	34,625	110,112	34,625
Purchase price (in dollars per share) | $ / shares				$ 16.51	$ 18.04	$ 15.17	$ 18.04
Share-based expense				$ 100	$ 100	$ 400	$ 100
Common stock available for future issuance (in shares) | shares				1,800,000		1,800,000
ATM Agreement
Equity Incentive Plans
Authorized value of stock under ATM agreement										$ 500,000
Number of shares issued (in shares) | shares				0		0	1,415,564
Proceeds from ATM Agreement							$ 33,300
Sale of stock average price (in dollars per share) | $ / shares					$ 23.54		$ 23.54
Commission costs under ATM agreement							$ 700