Fair Value of Financial Instruments - Valuation for Level 3 Assets (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 3,801,370	$ 3,935,253
Total (losses)/gains (realized/unrealized)
Included in earnings	54,963	(115,934)
Transfers out	(326)	(879)
Transfers to securitization trust, net	0	0
Funding/Contributions	21,948	19,191
Paydowns/Distributions	(294,927)	(330,853)
Sales	(166)	(320)
Purchases	88,521	782,477
Balance at the end of period	$ 3,671,383	$ 4,288,935
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income (Expense), Net	Other Operating Income (Expense), Net
Consolidated SLST \| VIE, Primary Beneficiary \| Residential loans
Total (losses)/gains (realized/unrealized)
Sales	$ 0
Residential loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,081,384	$ 1,703,290
Total (losses)/gains (realized/unrealized)
Included in earnings	(599)	(24,571)
Transfers out	(93)	(90)
Transfers to securitization trust, net	(86,110)	(598,430)
Funding/Contributions	0	0
Paydowns/Distributions	(141,355)	(126,575)
Sales		(320)
Purchases	67,939	767,914
Balance at the end of period	921,000	1,721,218
Residential loans \| Residential loans
Total (losses)/gains (realized/unrealized)
Sales	(166)
Residential loans \| Consolidated SLST \| VIE, Primary Beneficiary
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	827,582	1,070,882
Total (losses)/gains (realized/unrealized)
Included in earnings	15,121	(67,685)
Transfers out	0	0
Transfers to securitization trust, net	0	0
Funding/Contributions	0	0
Paydowns/Distributions	(13,550)	(33,344)
Sales		0
Purchases	0	0
Balance at the end of period	829,153	969,853
Residential loans held in securitization trusts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,616,114	801,429
Total (losses)/gains (realized/unrealized)
Included in earnings	33,041	(33,729)
Transfers out	(233)	(789)
Transfers to securitization trust, net	86,110	598,430
Funding/Contributions	0	0
Paydowns/Distributions	(130,911)	(117,548)
Sales		0
Purchases	20,582	14,563
Balance at the end of period	1,624,703	1,262,356
Residential loans held in securitization trusts \| Residential loans
Total (losses)/gains (realized/unrealized)
Sales	0
Multi-family loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	87,534	120,021
Total (losses)/gains (realized/unrealized)
Included in earnings	2,889	3,258
Transfers out	0	0
Transfers to securitization trust, net	0	0
Funding/Contributions	6,420	0
Paydowns/Distributions	(1,534)	(13,071)
Sales		0
Purchases	0	0
Balance at the end of period	95,309	110,208
Multi-family loans \| Multi-family loans
Total (losses)/gains (realized/unrealized)
Sales	0
Equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	179,746	239,631
Total (losses)/gains (realized/unrealized)
Included in earnings	3,451	6,793
Transfers out	0	0
Transfers to securitization trust, net	0	0
Funding/Contributions	15,528	19,191
Paydowns/Distributions	(7,577)	(40,315)
Sales		0
Purchases	0	0
Balance at the end of period	191,148	$ 225,300
Equity investments \| Equity investments
Total (losses)/gains (realized/unrealized)
Sales	0
Equity investments in disposal group held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	9,010
Total (losses)/gains (realized/unrealized)
Included in earnings	1,060
Transfers out	0
Transfers to securitization trust, net	0
Funding/Contributions	0
Paydowns/Distributions	0
Purchases	0
Balance at the end of period	$ 10,070

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Funding/Contributions

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers Out of Level 3 to Out of Securitization Trust, Net

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Indicates line item in statement in which net income is reported that includes gain (loss) from asset measured at fair value using unobservable input (level 3).

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