Real Estate Securities, Available for Sale - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2019 USD ($) securitization_trust	Jun. 30, 2020 USD ($) securitization_trust loan security	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) securitization_trust loan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Gross sales price of securities sold					$ 89,680	$ 0
Loss from sale of securities					57,045	0
Unrealized loss on real estate securities, available for sale		$ (58,510)		$ (7,863)	16,519	(17,621)
Unrealized gains (losses) in OCI		$ (58,500)		$ 7,900	$ 16,500	$ 17,600
Interest receivable							$ 700
Number of securitization trusts held | securitization_trust		2			2
Gross assets		$ 6,850,267			$ 6,850,267		7,414,306
Gross liabilities		4,849,430			4,849,430		5,212,956
Credit facilities | CMBS credit facilities
Debt Securities, Available-for-sale [Line Items]
Debt repaid		73,900
Primary beneficiary, securitization trust
Debt Securities, Available-for-sale [Line Items]
Number of securitization trusts sold | securitization_trust	1
Proceeds from sale of mortgage loans held in securitization trusts	$ 33,400
Gross assets	1,200,000	1,847,123			1,847,123		1,879,990
Gross liabilities	$ 1,200,000	1,764,579			1,764,579		1,769,181
Primary beneficiary
Debt Securities, Available-for-sale [Line Items]
Gross assets		3,878,068			3,878,068		3,502,341
Gross liabilities		3,219,819			3,219,819		3,117,364
Mortgage loans held in trust, unpaid principal balance		1,800,000			1,800,000		1,800,000
Mortgage obligations held in trust, unpaid principal balance		$ 1,600,000			$ 1,600,000		1,600,000
Number of underlying mortgage loans | loan		115			115
Weighted average coupon (in percentage)		4.50%			4.50%
Weighted average loan to value ratio (in percentage)		56.40%			56.40%
Difference between held and issued mortgage loans in securitization trusts		$ 81,600			$ 81,600		$ 110,100
Real estate securities, available for sale
Debt Securities, Available-for-sale [Line Items]
Number of securities sold | security		27
Gross sales price of securities sold		$ 89,700
Loss from sale of securities		57,000
Unrealized loss on real estate securities, available for sale			$ 36,400
Impairment loss on securities		29,200			$ 29,200
Weighted average contractual maturity					28 years 8 months 12 days
Expected maturity					5 years 7 months 6 days
Real estate securities, available for sale | Credit facilities | CMBS credit facilities
Debt Securities, Available-for-sale [Line Items]
Debt repaid		$ 66,100