Loans and Preferred Equity Held for Investment, net and Loans Held for Sale - Narrative (Details)	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Aug. 07, 2020 USD ($)	Jun. 30, 2020 USD ($) loan co-investment borrower	Mar. 31, 2020 USD ($) building loan	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) borrower loan investment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) property loan investment	Dec. 31, 2018 USD ($)	Mar. 31, 2018 loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity period of debt instruments depending upon the asset type (in years)					3 years 10 months 24 days
Interest receivable		$ 8,300,000			$ 8,300,000		$ 9,800,000
Provision for loan losses		(51,000)		$ 110,258,000	69,881,000	$ 110,258,000
Allowance for loan losses							272,600,000
Effect of CECL adoption					21,093,000	$ 0
Carrying value of loans							409,700,000
Assets-held-for-sale, including discontinued operations		$ 0			$ 0		$ 0
Real estate debt investments with contractual payments past due		1			1		5
Number of borrowers, contractual payments past due | borrower		1			1
Number of CRE debt investments contributed to more than 10% of interest income | investment					0
Percent of interest income contributed by investment					10.00%
Future funding commitments		$ 205,000,000.0			$ 205,000,000.0		$ 276,600,000
Unfunded lending commitments for loans held for sale		1,400,000			1,400,000
Allowance for lending commitments		$ 1,900,000			$ 1,900,000
Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Internal credit risk rating		3.9	3.8
Core
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses		$ 38,000,000.0
Number of loans classified as held-for-sale | loan					1
Core | Subsequent event
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of receivables	$ 105,200,000
COVID-19
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses			$ 36,800,000
NY hospitality loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses							$ 154,300,000	$ 53,800,000
Midwest hospitality | Subsequent event
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bridge loan	19,500,000
Midwest hospitality | Core | Subsequent event
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of receivables	24,500,000
Northeast Office Portfolio | Core
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses			$ 12,100,000		$ 20,900,000
Number of loans with potential loss | loan			1
Number of properties collateralized | building			6
Allowance for loan losses			$ 20,900,000
Effect of CECL adoption			8,800,000
Northeast Office Portfolio | Core | Subsequent event
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from collection on loans	80,700,000
West Hospitality | Core
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses			2,600,000
Gain (loss) on sales of loans, net		$ (32,800,000)
Allowance for loan losses			5,200,000
Effect of CECL adoption			$ 2,600,000
Number of loans classified as held-for-sale | co-investment		1
West Hospitality | Core | Subsequent event
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of receivables	105,200,000
Gain (loss) on sales of loans, net	$ (300,000)
Legacy, non-strategic portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans classified as held-for-sale | loan					1
Legacy, non-strategic portfolio | Legacy, Non-Strategic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans, non-accrual status | loan							1
Impaired financing receivable, recorded impairment							$ 10,600,000
Proceeds from sale of receivables		$ 8,300,000
Gain (loss) on sales of loans, net		3,700,000
NY hospitality loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans, non-accrual status | loan							4
NY hospitality loans | Legacy, non-strategic portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans, non-accrual status | loan			4						4
Commercial mortgage, regional mall loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses							$ 26,700,000	$ 8,800,000
Number of loans with potential loss | loan							3
Number of properties collateralized | property							2
Commercial mortgage, regional mall loans | Northeast Regional Mall B
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses							$ 10,500,000
Proceeds from sale of receivables			$ 9,200,000
Gain (loss) on sales of loans, net			1,800,000
Commercial mortgage, regional mall loans | West Regional Mall
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses							$ 18,500,000
Proceeds from sale of receivables		23,500,000
Gain (loss) on sales of loans, net		6,500,000
Number of loans with potential loss | loan							2
Number of properties collateralized | property							1
Commercial mortgage, regional mall loans | South Regional Mall A
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of receivables			22,000,000.0
Gain (loss) on sales of loans, net			(1,600,000)
Commercial mortgage, regional mall loans | South Regional Mall B
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of receivables			13,500,000
Gain (loss) on sales of loans, net			8,700,000
Commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of loans							$ 377,421,000
Future funding commitments		$ 205,000,000.0			$ 205,000,000.0
Hospitality | Midwest hospitality | Core
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans, non-accrual status | loan							1
Provision for loan losses			$ 2,300,000