Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Assets carried at fair value
Investment securities available for sale:	$ 24,284	$ 23,645
Derivative assets:
Total derivative assets	3,534	2,473
Derivative liabilities
Derivative assets	3,122	2,473
Variation Margin	(2,487)
Interest rate caps
Derivative assets:
Total derivative assets	2,002
Interest rate swaps
Derivative assets:
Total derivative assets	412	2,473
Derivative liabilities
Variation Margin	(2,487)
Fair Value, Measurements, Recurring
Assets carried at fair value
Fair Value	191,148	179,746
Assets of disposal group held for sale	32,870	38,428
Total	3,899,876	3,932,820
Derivative liabilities
Total	638,513	634,495
Fair Value, Measurements, Recurring \| Interest rate caps
Derivative assets:
Total derivative assets	2,002	2,473
Fair Value, Measurements, Recurring \| Option
Derivative assets:
Total derivative assets	1,120	0
Fair Value, Measurements, Recurring \| Interest rate swaps
Derivative liabilities
Derivative liability	0	0
Variation Margin	2,500
Fair Value, Measurements, Recurring \| Interest rate swaps \| Central Clearing House
Derivative liabilities
Derivative liability	2,900
Derivative assets	400
Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans, at fair value	921,000	1,081,384
Fair Value, Measurements, Recurring \| Residential loans \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans, at fair value	829,153	827,582
Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans, at fair value	1,624,703	1,616,114
Fair Value, Measurements, Recurring \| Multi-family loans
Assets carried at fair value
Multi-family loans	95,309	87,534
Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Investment securities available for sale:	107,200	0
Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Investment securities available for sale:	64,211	68,570
Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Investment securities available for sale:	30,668	30,133
Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Investment securities available for sale:	492	856
Fair Value, Measurements, Recurring \| Consolidated SLST CDOs \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Consolidated SLST CDOs	638,513	634,495
Level 1 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Fair Value	0	0
Assets of disposal group held for sale	0	0
Total	0	0
Derivative liabilities
Total	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Interest rate caps
Derivative assets:
Total derivative assets	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Option
Derivative assets:
Total derivative assets	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Derivative liabilities
Derivative liability	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 \| Consolidated SLST \| VIE, Primary Beneficiary
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
Assets carried at fair value
Multi-family loans	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 \| 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 \| Consolidated SLST CDOs \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Consolidated SLST CDOs	0	0
Level 2
Assets carried at fair value
Investment securities available for sale:	202,571	99,559
Derivative liabilities
Derivative assets	3,122	2,473
Level 2 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Fair Value	0	0
Assets of disposal group held for sale	22,800	29,418
Total	228,493	131,450
Derivative liabilities
Total	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Interest rate caps
Derivative assets:
Total derivative assets	2,002	2,473
Level 2 \| Fair Value, Measurements, Recurring \| Option
Derivative assets:
Total derivative assets	1,120	0
Level 2 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Derivative liabilities
Derivative liability	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Derivative Asset
Assets carried at fair value
Assets of disposal group held for sale	22,800	29,400
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 \| Consolidated SLST \| VIE, Primary Beneficiary
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
Assets carried at fair value
Multi-family loans	0	0
Level 2 \| Fair Value, Measurements, Recurring \| Agency RMBS
Assets carried at fair value
Investment securities available for sale:	107,200	0
Level 2 \| Fair Value, Measurements, Recurring \| Non-Agency RMBS
Assets carried at fair value
Investment securities available for sale:	64,211	68,570
Level 2 \| Fair Value, Measurements, Recurring \| CMBS
Assets carried at fair value
Investment securities available for sale:	30,668	30,133
Level 2 \| Fair Value, Measurements, Recurring \| ABS
Assets carried at fair value
Investment securities available for sale:	492	856
Level 2 \| Fair Value, Measurements, Recurring \| Consolidated SLST CDOs \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Consolidated SLST CDOs	0	0
Level 3
Assets carried at fair value
Fair Value	191,148	179,746
Level 3 \| Fair Value, Measurements, Recurring
Assets carried at fair value
Fair Value	191,148	179,746
Assets of disposal group held for sale	10,070	9,010
Total	3,671,383	3,801,370
Derivative liabilities
Total	638,513	634,495
Level 3 \| Fair Value, Measurements, Recurring \| Interest rate caps
Derivative assets:
Total derivative assets	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Option
Derivative assets:
Total derivative assets	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Derivative liabilities
Derivative liability	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans
Assets carried at fair value
Residential loans, at fair value	921,000	1,081,384
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans \| Consolidated SLST \| VIE, Primary Beneficiary
Assets carried at fair value
Residential loans, at fair value	829,153	827,582
Level 3 \| Fair Value, Measurements, Recurring \| Residential loans held in securitization trusts
Assets carried at fair value
Residential loans, at fair value	1,624,703	1,616,114
Level 3 \| Fair Value, Measurements, Recurring \| Multi-family loans
Assets carried at fair value
Multi-family loans	95,309	87,534
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 \| 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 \| Consolidated SLST CDOs \| Consolidated SLST \| VIE, Primary Beneficiary
Liabilities carried at fair value
Consolidated SLST CDOs	638,513	634,495
Level 3 \| Fair Value, Measurements, Recurring \| Equity investments
Assets carried at fair value
Assets of disposal group held for sale	$ 10,100	$ 9,000

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