Real Estate Owned - Narrative (Details)					3 Months Ended									9 Months Ended		12 Months Ended
		Aug. 03, 2022 USD ($)	Jun. 29, 2021 USD ($)	May 24, 2021 USD ($)	Sep. 30, 2023 USD ($) property	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2023 USD ($) property	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)
Real Estate [Line Items]
Number of real estate properties | property					2									2
Total carrying value, net					$ 7,974,031,000			$ 8,681,990,000						$ 7,974,031,000		$ 8,681,990,000
Debt related to real estate owned, held for investment, net					161,245,000			160,294,000						161,245,000		160,294,000
Increase in Specific CECL Allowance, net				$ 10,000,000						$ (10,000,000)		$ 20,000,000
Depreciation and amortization on real estate owned					1,020,000				$ 0					7,208,000	$ 704,000
Real estate held for sale, gain (loss) on reclassification														0
Total net revenue					500,000				1,100,000					4,300,000	5,300,000
Net realized loss on investment					0				$ 43,577,000					(86,604,000)	$ 43,577,000
Debt instrument, covenant, unencumbered liquidity, threshold					100,000,000									100,000,000
Debt instrument, covenant, net worth threshold					600,000,000									600,000,000
Write-offs, specific CECL allowance, funded														81,890,000		7,000,000
Financing receivable, loan specific, realized gain (loss) on writeoff							$ 7,000,000
Interest rate cap
Real Estate [Line Items]
Aggregate Notional Amount (in thousands)																			$ 1,100,000
Interest rate cap | Not Designated as Hedging Instrument
Real Estate [Line Items]
Aggregate Notional Amount (in thousands)					164,835,000			500,000,000						164,835,000		500,000,000
Derivative Financial Instruments, Assets | Interest rate cap | Not Designated as Hedging Instrument
Real Estate [Line Items]
Aggregate Notional Amount (in thousands)					2,200,000									$ 2,200,000
Hotel Through a Died-in-Lieu Foreclosure
Real Estate [Line Items]
Financing receivable, loan specific, realized gain (loss) on writeoff							4,800,000
Secured Overnight Financing Rate
Real Estate [Line Items]
Interest rate for repurchase facility														2.55%
Letter of Credit
Real Estate [Line Items]
Maximum amount of borrowings					388,400,000									$ 388,400,000
Line of credit facility, option to extend, period														1 year
Mortgages
Real Estate [Line Items]
Debt related to real estate owned, held for investment, net					161,200,000			160,300,000						$ 161,200,000		160,300,000
Less: deferred financing costs					3,600,000			4,500,000						3,600,000		4,500,000
JV Partner
Real Estate [Line Items]
Financing receivable, loan in process		$ 164,800,000
JV Partner | Joint venture
Real Estate [Line Items]
Equity method investment, ownership percentage		100.00%
Discontinued Operations, Held-for-Sale
Real Estate [Line Items]
Depreciation and amortization on real estate owned														4,000,000
Subordinate Mortgage Portfolio Segment
Real Estate [Line Items]
Total carrying value, net	[1],[2]				412,777,000			560,881,000						412,777,000		560,881,000
Commercial Mortgage and Subordinated Portfolio Segment
Real Estate [Line Items]
Total carrying value, net					102,600,000			138,300,000						102,600,000		138,300,000
Increase in Specific CECL Allowance, net														59,500,000
Realized loss on investments																	$ 20,000,000
Write-offs, specific CECL allowance, funded						$ 81,980,000
Mezzanine Loans | Subordinate Mortgage Portfolio Segment
Real Estate [Line Items]
Increase in Specific CECL Allowance, net													$ 10,000,000
Hotel - Washington D.C.
Real Estate [Line Items]
Increase in Specific CECL Allowance, net																	$ 10,000,000
Net assets acquired					153,200,000			155,900,000						153,200,000		155,900,000
Hotel - Washington D.C. | Subordinate Mortgage Portfolio Segment
Real Estate [Line Items]
Debt related to real estate owned, held for investment, net				110,000,000																$ 110,000,000
Payments for mortgage loans			$ 110,000,000
Hotel - Washington D.C. | Junior Mezzanine Loans
Real Estate [Line Items]
Total carrying value, net																				20,000,000
Hotel - Washington D.C. | Senior Mezzanine Loans
Real Estate [Line Items]
Total carrying value, net																				$ 24,500,000
Payments to acquire mortgage notes receivable				$ 24,500,000
Multifamily Development - Brooklyn, NY | Subordinate Mortgage Portfolio Segment
Real Estate [Line Items]
Debt related to real estate owned, held for investment, net																					$ 122,200,000
Increase in Specific CECL Allowance, net																		$ 30,000,000
Multifamily Development - Brooklyn, NY | Commercial Mortgage and Subordinated Portfolio Segment
Real Estate [Line Items]
Increase in Specific CECL Allowance, net										10,000,000
Deed-In-Lieu Of Foreclosure
Real Estate [Line Items]
Total carrying value, net		$ 226,500,000			349,300,000			302,700,000						349,300,000		$ 302,700,000
Real estate investment property, net		270,100,000
Net realized loss on investment		$ 43,600,000
Financing receivable, construction and finance costs capitalized					17,600,000									46,700,000
Residential-for-Sale - Manhattan, NY
Real Estate [Line Items]
Write-offs, specific CECL allowance, funded								$ 7,000,000		7,000,000
Residential-for-Sale - Manhattan, NY | Commercial Mortgage and Subordinated Portfolio Segment
Real Estate [Line Items]
Increase in Specific CECL Allowance, net											$ 30,000,000
Hotel - Atlanta, GA
Real Estate [Line Items]
Total net revenue					500,000									1,900,000
Real estate investment property, net					$ 75,300,000		$ 75,000,000							$ 75,300,000
Hotel - Atlanta, GA | Commercial Mortgage and Subordinated Portfolio Segment
Real Estate [Line Items]
Increase in Specific CECL Allowance, net										$ 7,000,000

[1] Includes $213,139 and $191,608 pledged as collateral under secured debt arrangements in 2023 and 2022, respectively.

[2] Net of $220,305 and $159,724 CECL Allowance in 2023 and 2022, respectively, comprised of $193,000 and $133,500 Specific CECL Allowance and $27,305 and $26,224 General CECL Allowance, respectively.