Fair Value of Financial Instruments - Valuation for Level 3 Assets (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 3,671,383	$ 4,288,935	$ 3,801,370	$ 3,935,253
Total (losses)/gains (realized/unrealized)
Included in earnings	(22,424)	(60,338)	32,539	(176,272)
Transfers out	(4,168)	(976)	(4,494)	(1,855)
Transfers to securitization trust, net	0	0	0	0
Funding/Contributions	8,985		30,933	19,191
Paydowns/Distributions	(348,917)	(341,533)	(643,844)	(672,386)
Sales	(441)	320	(607)
Purchases	106,266	773,260	194,787	1,555,737
Balance at the end of period	$ 3,410,684	$ 4,659,668	$ 3,410,684	$ 4,659,668
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 \| Residential loans
Total (losses)/gains (realized/unrealized)
Sales	$ 0		$ 0
Residential loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	921,000	$ 1,721,218	1,081,384	$ 1,703,290
Total (losses)/gains (realized/unrealized)
Included in earnings	772	(28,405)	173	(52,976)
Transfers out	(2,664)	(785)	(2,757)	(875)
Transfers to securitization trust, net	(103,972)	(78,130)	(190,082)	(676,560)
Funding/Contributions	0		0	0
Paydowns/Distributions	(144,017)	(166,989)	(285,372)	(293,564)
Sales		320
Purchases	86,145	746,090	154,084	1,514,004
Balance at the end of period	757,264	2,193,319	757,264	2,193,319
Residential loans \| Residential loans
Total (losses)/gains (realized/unrealized)
Sales	0		(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	829,153	969,853	827,582	1,070,882
Total (losses)/gains (realized/unrealized)
Included in earnings	(24,154)	(11,607)	(9,033)	(79,292)
Transfers out	0	0	0	0
Transfers to securitization trust, net	0	0	0	0
Funding/Contributions	0		0	0
Paydowns/Distributions	(15,030)	(37,468)	(28,580)	(70,812)
Sales		0
Purchases	0	0	0	0
Balance at the end of period	789,969	920,778	789,969	920,778
Residential loans held in securitization trusts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,624,703	1,262,356	1,616,114	801,429
Total (losses)/gains (realized/unrealized)
Included in earnings	(5,139)	(32,206)	27,902	(65,935)
Transfers out	(1,504)	(191)	(1,737)	(980)
Transfers to securitization trust, net	103,972	78,130	190,082	676,560
Funding/Contributions	0		0	0
Paydowns/Distributions	(152,133)	(120,164)	(283,044)	(237,712)
Sales		0
Purchases	20,121	27,170	40,703	41,733
Balance at the end of period	1,589,579	1,215,095	1,589,579	1,215,095
Residential loans held in securitization trusts \| Residential loans
Total (losses)/gains (realized/unrealized)
Sales	(441)		(441)
Multi-family loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	95,309	110,208	87,534	120,021
Total (losses)/gains (realized/unrealized)
Included in earnings	3,440	3,040	6,329	6,298
Transfers out	0	0	0	0
Transfers to securitization trust, net	0	0	0	0
Funding/Contributions	8,985		15,405	0
Paydowns/Distributions	(10,312)	(6,423)	(11,846)	(19,494)
Sales		0
Purchases	0	0	0	0
Balance at the end of period	97,422	106,825	97,422	106,825
Multi-family loans \| Multi-family loans
Total (losses)/gains (realized/unrealized)
Sales	0		0
Equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	191,148	225,300	179,746	239,631
Total (losses)/gains (realized/unrealized)
Included in earnings	5,032	8,840	8,483	15,633
Transfers out	0	0	0	0
Transfers to securitization trust, net	0	0	0	0
Funding/Contributions	0		15,528	19,191
Paydowns/Distributions	(27,425)	(10,489)	(35,002)	(50,804)
Sales		0
Purchases	0	0	0	0
Balance at the end of period	168,755	$ 223,651	168,755	$ 223,651
Equity investments \| Equity investments
Total (losses)/gains (realized/unrealized)
Sales	0		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	10,070		9,010
Total (losses)/gains (realized/unrealized)
Included in earnings	(2,375)		(1,315)
Transfers out	0		0
Transfers to securitization trust, net	0		0
Funding/Contributions	0		0
Paydowns/Distributions	0		0
Purchases	0		0
Balance at the end of period	$ 7,695		$ 7,695

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-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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