Fair Value of Financial Instruments - Valuation for Level 3 Assets (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 3,410,684	$ 4,659,668	$ 3,801,370	$ 3,935,253
Total (losses)/gains (realized/unrealized)
Included in earnings	(45,726)	(156,506)	(13,188)	(332,778)
Transfers out	(9,419)	(886)	(13,913)	(2,741)
Transfers to securitization trust, net	0	0	0	0
Transfer to disposal group held for sale		0		0
Funding/Contributions	9,390	8,895	40,323	28,086
Paydowns/Distributions	(281,168)	(366,987)	(925,012)	(1,039,373)
Sales	(18,604)	0	(19,210)
Purchases	187,829	100,571	382,616	1,656,308
Balance at the end of period	$ 3,252,986	$ 4,244,755	$ 3,252,986	$ 4,244,755
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	Other Operating Income (Expense), Net	Other Operating Income (Expense), Net
Consolidated SLST \| VIE, Primary Beneficiary
Total (losses)/gains (realized/unrealized)
Sales			$ 0
Purchases				$ 0
Residential loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 757,264	$ 2,193,319	1,081,384	1,703,290
Total (losses)/gains (realized/unrealized)
Included in earnings	(7,392)	(56,870)	(7,220)	(109,846)
Transfers out	(7,441)	(636)	(10,198)	(1,511)
Transfers to securitization trust, net	(54,332)	(373,113)	(244,414)	(1,049,673)
Transfer to disposal group held for sale		0		0
Funding/Contributions	0	0	0	0
Paydowns/Distributions	(103,660)	(175,105)	(389,032)	(468,669)
Sales	(18,604)	0	(18,769)
Purchases	171,104	73,723	325,188	1,587,727
Balance at the end of period	736,939	1,661,318	736,939	1,661,318
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	789,969	920,778	827,582	1,070,882
Total (losses)/gains (realized/unrealized)
Included in earnings	(31,425)	(33,965)	(40,458)	(113,257)
Transfers out	0	0	0	0
Transfers to securitization trust, net	0	0	0	0
Transfer to disposal group held for sale		0		0
Funding/Contributions	0	0	0	0
Paydowns/Distributions	(15,940)	(26,028)	(44,520)	(96,840)
Sales	0	0
Purchases	0	0	0
Balance at the end of period	742,604	860,785	742,604	860,785
Residential loans held in securitization trusts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,589,579	1,215,095	1,616,114	801,429
Total (losses)/gains (realized/unrealized)
Included in earnings	(11,788)	(64,282)	16,114	(130,217)
Transfers out	(1,978)	(250)	(3,715)	(1,230)
Transfers to securitization trust, net	54,332	373,113	244,414	1,049,673
Transfer to disposal group held for sale		0		0
Funding/Contributions	0	0	0	0
Paydowns/Distributions	(132,518)	(139,451)	(415,562)	(377,163)
Sales	0	0	(441)
Purchases	16,725	26,848	57,428	68,581
Balance at the end of period	1,514,352	1,411,073	1,514,352	1,411,073
Multi-family loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	97,422	106,825	87,534	120,021
Total (losses)/gains (realized/unrealized)
Included in earnings	2,695	360	9,024	6,658
Transfers out	0	0	0	0
Transfers to securitization trust, net	0	0	0	0
Transfer to disposal group held for sale		0		0
Funding/Contributions	0	0	15,405	0
Paydowns/Distributions	(1,682)	(11,356)	(13,528)	(30,850)
Sales	0	0	0
Purchases	0	0	0	0
Balance at the end of period	98,435	95,829	98,435	95,829
Equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	168,755	223,651	179,746	239,631
Total (losses)/gains (realized/unrealized)
Included in earnings	4,806	(1,749)	13,289	13,884
Transfers out	0	0	0	0
Transfers to securitization trust, net	0	0	0	0
Transfer to disposal group held for sale		(9,936)		(9,936)
Funding/Contributions	9,390	8,895	24,918	28,086
Paydowns/Distributions	(27,368)	(15,047)	(62,370)	(65,851)
Sales	0	0	0
Purchases	0	0	0	0
Balance at the end of period	155,583	205,814	155,583	205,814
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	7,695	0	9,010	0
Total (losses)/gains (realized/unrealized)
Included in earnings	(2,622)	0	(3,937)	0
Transfers out	0		0	0
Transfers to securitization trust, net	0	0	0	0
Transfer to disposal group held for sale		9,936		9,936
Funding/Contributions	0	0	0	0
Paydowns/Distributions	0	0	0	0
Sales	0	0	0
Purchases	0	0	0	0
Balance at the end of period	$ 5,073	$ 9,936	$ 5,073	$ 9,936

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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- Definition

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
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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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
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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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.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-SubTopic 10
-Topic 820
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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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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