Fair Value - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) measurement_input	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) measurement_input	Sep. 30, 2019 USD ($)	Dec. 31, 2019 measurement_input
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized (gain) loss on mortgage loans and obligations held in securitization trusts, net | $	$ 13,162,000	$ 1,976,000	$ 41,589,000	$ (4,602,000)
Terminal Capitalization Rate | Minimum | Legacy, Non-Strategic
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment property, net, measurement input (in percentage)	0.06		0.06
Terminal Capitalization Rate | Maximum | Legacy, Non-Strategic
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment property, net, measurement input (in percentage)	0.16		0.16
Mortgage loans held in securitization trusts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain on securitization of assets | $	$ 0	$ 2,700,000	$ 0	$ 2,800,000
Level 3 | Recurring | Investments in unconsolidated ventures - PE Investments | Discount Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
PE investment, measurement input	0.110		0.110		0.110
Level 3 | Recurring | Investments in unconsolidated ventures - PE Investments | Discount Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
PE investment, measurement input	0.120		0.120		0.120
Level 3 | Recurring | Mortgage obligations issued by securitization trusts | Measurement Input, Yield | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.203		0.203		0.150
Level 3 | Recurring | Mortgage obligations issued by securitization trusts | Measurement Input, Yield | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.543		0.543		0.161
Level 3 | Recurring | Mortgage obligations issued by securitization trusts | Measurement Input, Expected Term | Weighted average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average expected maturity of CRE securities			5 years 1 month 6 days		5 years 4 months 24 days