Loans and Preferred Equity Held for Investment, net - Activity in Loans Held for Investment, Net (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at January 1, 2020			$ 2,576,332
Acquisitions/originations/additional funding		$ 121,309
Loan maturities/principal repayments		(373,285)
Transfer to loans held for sale		(154,370)
Discount accretion/premium amortization		6,047
Capitalized interest		(3,856)
Provision for loan losses		(86,329)
Effect of CECL adoption		(21,093)
Charge-off		38,659
Balance at end of period		2,103,414
Provision for loan losses transferred to held for sale	$ 5,200
Net impairment		1,800
PD/LGD model
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Unfunded commitments		$ 1,000