Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Assets carried at fair value
Investment securities available for sale	$ 498,805,000	$ 1,760,812,000
Interest rate swaps
Liabilities carried at fair value
Derivative labilities		(29,000,000.0)
Variation margin		44,800,000
Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	901,899,000
Agency CMBS
Assets carried at fair value
Investment securities available for sale	0	20,277,000
Fair Value, Measurements, Recurring
Assets carried at fair value
Investments in unconsolidated entities	214,289,000	83,882,000
Preferred equity and mezzanine loan investments	180,850,000	0
Total	4,114,175,000	22,681,286,000
Liabilities carried at fair value
Total	1,088,233,000	17,777,280,000
Fair Value, Measurements, Recurring \| Interest rate swaps
Assets carried at fair value
Derivative assets	0	15,878,000
Fair Value, Measurements, Recurring \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans, at fair value	1,274,850,000	1,328,886,000
Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	922,877,000
Fair Value, Measurements, Recurring \| Agency CMBS
Assets carried at fair value
Investment securities available for sale	0	50,958,000
Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Investment securities available for sale	630,196,000	715,314,000
Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Investment securities available for sale	288,112,000	267,777,000
Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Investment securities available for sale	42,500,000	49,214,000
Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans, at fair value	1,442,685,000	1,429,754,000
Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans, at fair value	40,693,000	0
Fair Value, Measurements, Recurring \| Multi-family loans held in securitization trusts
Assets carried at fair value
Multi-family loans held in securitization trusts	0	17,816,746,000
Fair Value, Measurements, Recurring \| Multi-family collateralized debt obligations, at fair value
Liabilities carried at fair value
Collateralized debt obligations, at fair value	0	16,724,451,000
Fair Value, Measurements, Recurring \| Residential collateralized debt obligations, at fair value
Liabilities carried at fair value
Collateralized debt obligations, at fair value	1,088,233,000	1,052,829,000
Level 1 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Investments in unconsolidated entities	0
Total	0	0
Liabilities carried at fair value
Total	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Assets carried at fair value
Derivative assets	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Agency CMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Investment securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans, at fair value	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans, at fair value	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Multi-family loans held in securitization trusts
Assets carried at fair value
Multi-family loans held in securitization trusts	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Multi-family collateralized debt obligations, at fair value
Liabilities carried at fair value
Collateralized debt obligations, at fair value	0	0
Level 2
Assets carried at fair value
Investment securities available for sale	960,808,000	2,006,140,000
Level 2 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Investments in unconsolidated entities	0
Total	960,808,000	2,022,018,000
Liabilities carried at fair value
Total	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Assets carried at fair value
Derivative assets	0	15,878,000
Level 2 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	922,877,000
Level 2 \| Fair Value, Measurements, Recurring \| Agency CMBS
Assets carried at fair value
Investment securities available for sale	0	50,958,000
Level 2 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Investment securities available for sale	630,196,000	715,314,000
Level 2 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Investment securities available for sale	288,112,000	267,777,000
Level 2 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Investment securities available for sale	42,500,000	49,214,000
Level 2 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans, at fair value	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans, at fair value	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Multi-family loans held in securitization trusts
Assets carried at fair value
Multi-family loans held in securitization trusts	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Multi-family collateralized debt obligations, at fair value
Liabilities carried at fair value
Collateralized debt obligations, at fair value	0	0
Level 3
Assets carried at fair value
Investments in unconsolidated entities	214,289,000	191,359,000
Level 3 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Investments in unconsolidated entities	214,289,000	83,882,000
Preferred equity and mezzanine loan investments	180,850,000	0
Total	3,153,367,000	20,659,268,000
Liabilities carried at fair value
Total	1,088,233,000	17,777,280,000
Level 3 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Assets carried at fair value
Derivative assets	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans, at fair value	1,274,850,000	1,328,886,000
Level 3 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Agency CMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Investment securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Investment securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans, at fair value	1,442,685,000	1,429,754,000
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans, at fair value	40,693,000	0
Level 3 \| Fair Value, Measurements, Recurring \| Multi-family loans held in securitization trusts
Assets carried at fair value
Multi-family loans held in securitization trusts	0	17,816,746,000
Level 3 \| Fair Value, Measurements, Recurring \| Multi-family collateralized debt obligations, at fair value
Liabilities carried at fair value
Collateralized debt obligations, at fair value	0	16,724,451,000
Level 3 \| Fair Value, Measurements, Recurring \| Residential collateralized debt obligations, at fair value
Liabilities carried at fair value
Collateralized debt obligations, at fair value	$ 1,088,233,000	$ 1,052,829,000

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Financial Instrument Owned, Loans And Preferred Equity

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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