Loans and Preferred Equity Held for Investment, net and Loans Held for Sale - Summary of Loans Held for Investment, Net (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 2,301,950	$ 2,858,423
Loan carrying value		2,295,095
Allowance for loan losses		(52,521)	(272,624)	$ (172,894)	$ (109,328)
Total	[1]	2,242,574	2,576,332
Fixed rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		268,002	351,351
Variable rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		2,033,948	2,507,072
Commercial mortgage
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		2,301,950	2,858,423
Total		2,295,095	2,848,956
Mezzanine loans | Fixed rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 135,389	$ 223,395
Weighted average coupon (in percentage)		12.80%	12.80%
Weighted average maturity in years		4 years 6 months	4 years 2 months 12 days
Mezzanine loans | Variable rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 15,462	$ 38,110
Weighted average coupon (in percentage)		10.10%	11.40%
Weighted average maturity in years		2 years 2 months 12 days	2 years
Preferred equity interests | Fixed rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 118,715	$ 115,384
Weighted average coupon (in percentage)		12.50%	12.50%
Weighted average maturity in years		6 years 4 months 24 days	6 years 10 months 24 days
Other loans | Fixed rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 13,898	$ 12,572
Weighted average coupon (in percentage)		15.00%	15.00%
Weighted average maturity in years		3 years 10 months 24 days	4 years 4 months 24 days
Senior loans | Variable rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 1,011,334	$ 1,462,467
Weighted average coupon (in percentage)		5.40%	6.00%
Weighted average maturity in years		3 years 7 months 6 days	3 years 9 months 18 days
Securitized loans | Variable rate
Financing Receivable, Impaired [Line Items]
Principal amount, financial assets		$ 1,007,152	$ 1,006,495
Weighted average coupon (in percentage)		5.10%	5.20%
Weighted average maturity in years		3 years 9 months 18 days	4 years 2 months 12 days
Loans and preferred equity held for investment | Fixed rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		$ 267,150	$ 350,264
Loans and preferred equity held for investment | Variable rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		2,027,945	2,498,692
Loans and preferred equity held for investment | Commercial mortgage
Financing Receivable, Impaired [Line Items]
Loan carrying value		2,295,095	2,848,956
Loans and preferred equity held for investment | Mezzanine loans | Fixed rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		134,654	222,503
Loans and preferred equity held for investment | Mezzanine loans | Variable rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		15,582	38,258
Loans and preferred equity held for investment | Preferred equity interests | Fixed rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		118,696	115,313
Loans and preferred equity held for investment | Other loans | Fixed rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		13,800	12,448
Loans and preferred equity held for investment | Senior loans | Variable rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		1,008,062	1,457,738
Loans and preferred equity held for investment | Securitized loans | Variable rate
Financing Receivable, Impaired [Line Items]
Loan carrying value		$ 1,004,301	$ 1,002,696

[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.