Debt and Preferred Equity Investments - Schedule of Activity in Debt and Preferred Equity Investments (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2024 USD ($) investment	Dec. 31, 2023 USD ($) investment
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 346,745	$ 623,280
Redemptions/sales/syndications/equity ownership/amortization	(64,629)	(349,947)
Net change in loan loss reserves	0	(6,890)
Balance at end of period	$ 293,924	$ 346,745
Number of investments, nonperforming | investment	2	2
Carrying Value	$ 293,924	$ 346,745
Preferred Equity (4)
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Carrying Value	134,474
Preferred Equity (4) | 625 Madison Avenue
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Carrying Value	209,900
Total floating rate
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Carrying Value	109,604	168,899
Alternative Strategy Portfolio (3) | Total floating rate
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Carrying Value	49,800
Debt Investment
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/Accretion	5,334	72,160
Preferred Equity Investments
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/Accretion	$ 6,474	$ 8,142