Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Measurements, Recurring
Assets carried at fair value
Equity investments	$ 239,631	$ 259,095
Total	4,136,097	4,196,580
Liabilities carried at fair value
Total	839,419	1,054,335
Fair Value, Measurements, Recurring \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans:	1,070,882	1,266,785
Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans:	1,703,290	1,090,930
Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans:	801,429	691,451
Fair Value, Measurements, Recurring \| Multi-family loans
Assets carried at fair value
Multi-family loans	120,021	163,593
Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	139,395
Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	128,019	355,666
Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Debt Securities, Available-for-sale	33,146	186,440
Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Debt Securities, Available-for-sale	39,679	43,225
Fair Value, Measurements, Recurring \| Residential collateralized debt obligations, at fair value \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Multi-family collateralized debt obligations	839,419	1,054,335
Level 1 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Equity investments	0	0
Total	0	0
Liabilities carried at fair value
Total	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans:	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans:	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans:	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Multi-family loans
Assets carried at fair value
Multi-family loans	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Residential collateralized debt obligations, at fair value \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Multi-family collateralized debt obligations	0	0
Level 2
Assets carried at fair value
Debt Securities, Available-for-sale	200,844	724,726
Level 2 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Equity investments	0	0
Total	200,844	724,726
Liabilities carried at fair value
Total	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans:	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans:	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans:	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Multi-family loans
Assets carried at fair value
Multi-family loans	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	139,395
Level 2 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	128,019	355,666
Level 2 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Debt Securities, Available-for-sale	33,146	186,440
Level 2 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Debt Securities, Available-for-sale	39,679	43,225
Level 2 \| Fair Value, Measurements, Recurring \| Residential collateralized debt obligations, at fair value \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Multi-family collateralized debt obligations	0	0
Level 3
Assets carried at fair value
Equity investments	239,631	259,095
Level 3 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Equity investments	239,631	259,095
Total	3,935,253	3,471,854
Liabilities carried at fair value
Total	839,419	1,054,335
Level 3 \| Fair Value, Measurements, Recurring \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans:	1,070,882	1,266,785
Liabilities carried at fair value
Multi-family collateralized debt obligations		1,054,335
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans:	1,703,290	1,090,930
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans:	801,429	691,451
Level 3 \| Fair Value, Measurements, Recurring \| Multi-family loans
Assets carried at fair value
Multi-family loans	120,021	163,593
Level 3 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Debt Securities, Available-for-sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Residential collateralized debt obligations, at fair value \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Multi-family collateralized debt obligations	$ 839,419	$ 1,054,335

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