Loans and Preferred Equity Held for Investment, net and Loans Held for Sale - Impaired Loans (Details) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross carrying value with allowance for loan losses					$ 409,700
Loans and preferred equity held for investment, net	[1]			$ 2,242,574	2,576,332
Commercial mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Unpaid principal balance					408,058
Gross carrying value with allowance for loan losses					377,421
Gross carrying value without allowance for loan losses					32,322
Gross carrying value total					409,743
Allowance for loan losses					272,624
Loans and preferred equity held for investment, net				2,295,095	2,848,956
Average carrying value before allowance for loan losses		$ 320,934	$ 389,500
Interest income		$ 1,305	$ 2,651
Commercial mortgage | 90 Days or More Past Due / Nonaccrual
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and preferred equity held for investment, net				$ 29,846	258,129
Commercial mortgage, hospitality loan | 90 Days or More Past Due / Nonaccrual | First mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and preferred equity held for investment, net					258,100
Commercial mortgage, hospitality loan | 90 Days or More Past Due / Nonaccrual | Hotel | Hotel, New York
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and preferred equity held for investment, net					$ 257,200
Commercial mortgage, hospitality loan | 90 Days or More Past Due / Nonaccrual | Hotel | Hotel, New York | First mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Number of loans, non-accrual status | loan					4

[1] Net of $52.5 million and $272.6 million of allowance for loan losses at June 30, 2020 and December 31, 2019, respectively. See Note 3, “Loans and Preferred Equity Held for Investments, net and Loans Held for Sale” for further details.