Borrowings (Details) $ in Thousands				9 Months Ended	12 Months Ended
		Feb. 13, 2019	Aug. 18, 2017 USD ($)	Sep. 30, 2021 USD ($) counterparty	Dec. 31, 2020 USD ($) counterparty
Borrowings [Line Items]
Total secured borrowings				$ 3,100,000	$ 2,300,000
Number of Counterparties with Outstanding Reverse Repurchase Agreements | counterparty				24	24
Financial Instruments transferred as collateral for repurchase agreements				$ 2,400,000	$ 1,800,000
Collateral on repurchase agreements, unsettled sales				$ 3,000	1,400
Repurchase Agreements amount at risk threshold				10.00%
Other secured borrowings	[1]			$ 90,981	51,062
Other secured borrowings, at fair value	[1]			$ 872,306	$ 754,921
Minimum
Borrowings [Line Items]
Reverse Repurchase Agreements Maturity				30 days
Repurchase agreements, remaining days to maturity				1 day	4 days
Repurchase Agreements Interest Rate				0.10%	0.20%
Maximum
Borrowings [Line Items]
Reverse Repurchase Agreements Maturity				364 days
Repurchase agreements, remaining days to maturity				730 days	516 days
Repurchase Agreements Interest Rate				3.75%	5.00%
Reverse repurchase agreements
Borrowings [Line Items]
Cash collateral posted for securities sold under agreements to repurchase				$ 57,000	$ 28,900
Securitized residential mortgage loans
Borrowings [Line Items]
Fair Value of Assets Transfered and Accounted for as Secured Borrowings				917,300	801,300
Secured borrowing recourse facility collateralized by unsecured loan portfolio
Borrowings [Line Items]
Other secured borrowings				$ 3,800	$ 8,700
Debt Instrument, Interest Rate, Effective Rate				2.01%	2.30%
Secured borrowing recourse facility collateralized by unsecured loan portfolio | Unsecured loans
Borrowings [Line Items]
Fair Value of Assets Transfered and Accounted for as Secured Borrowings				$ 5,700	$ 11,500
Non-QM loan securitization
Borrowings [Line Items]
Other secured borrowings					$ 754,900
Debt Instrument, Interest Rate, Effective Rate				1.73%	2.43%
Secured borrowing facility collateralized by unsecured loan portfolio
Borrowings [Line Items]
Other secured borrowings				$ 31,800	$ 7,000
Debt Instrument, Interest Rate, Effective Rate				2.25%	2.25%
Secured borrowing facility collateralized by unsecured loan portfolio | Unsecured loans
Borrowings [Line Items]
Fair Value of Assets Transfered and Accounted for as Secured Borrowings				$ 48,800	$ 31,800
Secured borrowing facility collateralized by ABS backed by consumer loans [Member]
Borrowings [Line Items]
Other secured borrowings				$ 46,400	$ 28,700
Debt Instrument, Interest Rate, Effective Rate				4.70%	5.22%
Fair Value of Assets Transfered and Accounted for as Secured Borrowings				$ 64,400	$ 44,500
Commercial mortgage loans
Borrowings [Line Items]
Other secured borrowings				7,500	6,700
Fair Value of Assets Transfered and Accounted for as Secured Borrowings				18,000	$ 17,300
Loan Participations and Assignments
Borrowings [Line Items]
Other secured borrowings				$ 1,500
Debt Instrument, Interest Rate, Effective Rate				3.20%
Fair Value of Assets Transfered and Accounted for as Secured Borrowings				$ 1,800
Senior Notes
Borrowings [Line Items]
Debt Instrument, Interest Rate, Effective Rate				5.80%
Debt Instrument, Face Amount			$ 86,000
Debt Instrument, Interest Rate, Stated Percentage		5.50%
Redemption percentage		100.00%
Debt Instrument, Maturity Date			Sep. 01, 2022

[1] Ellington Financial Inc.'s Condensed Consolidated Balance Sheet includes assets and liabilities of variable interest entities it has consolidated. See Note 9 for additional details on Ellington Financial Inc.'s consolidated variable interest entities.