Loans and Preferred Equity Held for Investment, net - Nonaccrual and Past Due Loans (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) loan
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net	$ 2,103,414	$ 2,576,332
Midwest hospitality
Financing Receivable, Past Due [Line Items]
Bridge loan	19,500
Commercial mortgage
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net	2,143,938	2,848,956
Commercial mortgage | Current or Less Than 30 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net	2,143,938	2,558,505
Commercial mortgage | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net	0	32,322
Commercial mortgage | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net	0	0
Commercial mortgage | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net	$ 0	$ 258,129
Hospitality | Core | Midwest hospitality
Financing Receivable, Past Due [Line Items]
Number of loans, non-accrual status | loan		1
Hospitality | 30-59 Days Past Due | Core | Midwest hospitality
Financing Receivable, Past Due [Line Items]
Number of loans, non-accrual status | loan		1
NY hospitality loans
Financing Receivable, Past Due [Line Items]
Number of loans, non-accrual status | loan		4
Commercial mortgage, hospitality loan | 90 Days or More Past Due | First mortgage loans
Financing Receivable, Past Due [Line Items]
Loans and preferred equity held for investment, net		$ 258,100