Subsequent Events (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 06, 2020 USD ($) property security	Sep. 30, 2020 USD ($) security	Jun. 30, 2020 USD ($)	Sep. 30, 2020 USD ($) property security	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Subsequent Event [Line Items]
Number of real estate properties | property				11
Gain on sale of properties				$ 9,240,000	$ 0
Gross sales price of securities sold				118,586,000	$ 0
Allowance for loan losses						$ 272,600,000
Principal amount		$ 2,556,443,000		2,556,443,000		3,199,923,000
Credit facilities
Subsequent Event [Line Items]
Principal amount		608,632,000		608,632,000		1,099,233,000
CMBS credit facilities | Credit facilities
Subsequent Event [Line Items]
Debt repaid			$ 73,900,000	79,200,000
Principal amount		$ 25,232,000		$ 25,232,000		205,522,000
Interest rate		4.25%		4.25%
Master repurchase facilities | Credit facilities
Subsequent Event [Line Items]
Principal amount		$ 583,400,000		$ 583,400,000		780,211,000
Maximum borrowing capacity		2,250,000,000		2,250,000,000
Master repurchase facilities | Credit facilities | Bank 2 facility 3
Subsequent Event [Line Items]
Principal amount		21,353,000		21,353,000		$ 22,750,000
Maximum borrowing capacity		$ 200,000,000		$ 200,000,000
CRE securities
Subsequent Event [Line Items]
Number of securities sold | security		5		32
Gross sales price of securities sold		$ 28,800,000		$ 118,500,000
Gain from sale of securities		5,200,000
Core
Subsequent Event [Line Items]
Allowance for loan losses		$ 1,600,000		$ 1,600,000
Subsequent event | Senior loan | Secured by Office Property
Subsequent Event [Line Items]
Principal amount	$ 22,800,000
Interest rate	3.60%
Subsequent event | Master repurchase facilities | Credit facilities | Bank 2 facility 3
Subsequent Event [Line Items]
Extension period	1 year
Maximum borrowing capacity	$ 21,400,000
Subsequent event | CRE securities
Subsequent Event [Line Items]
Number of securities sold | security	6
Gross sales price of securities sold	$ 14,700,000
Gain from sale of securities	3,600,000
Subsequent event | CRE securities | CMBS credit facilities
Subsequent Event [Line Items]
Debt repaid	$ 6,600,000
Subsequent event | Legacy, Non-Strategic
Subsequent Event [Line Items]
Number of real estate properties | property	14
Gross proceeds from sale of real estate properties	$ 29,300,000
Net proceeds from sale of real estate properties	27,300,000
Gain on sale of properties	(2,000,000.0)
Subsequent event | Core | Corporate term loans
Subsequent Event [Line Items]
Proceeds from collection on loans	$ 12,100,000