Equity - Narrative (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2024 shares	Mar. 31, 2024 USD ($) entity $ / shares shares	Mar. 31, 2023 USD ($) shares	Dec. 31, 2023 entity $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2020 $ / shares shares	Feb. 28, 2020 USD ($)
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		36,992,019		27,460,161
Common stock, par value per share (in dollars per share) | $ / shares		$ 0.01		$ 0.01
Common stock, shares authorized (in shares)		125,000,000		125,000,000
Preferred stock, par value per share (in dollars per share) | $ / shares					$ 25.00
Preferred stock payable | $		$ 12,600,000
Preferred stock, shares authorized (in shares)		25,000,000		25,000,000
Common stock authorized | $							$ 25,000,000
Treasury stock, common (in shares)		(1,035,785)		(1,035,785)
Sale of common stock, net of offering costs | $		$ 0	$ 2,427,000
Number of non controlling interest subsidiaries | entity		3		3
Open market purchases
Class of Stock [Line Items]
Treasury stock, common (in shares)		(525,039)		(525,039)
At-the-Market Program
Class of Stock [Line Items]
Common stock authorized | $		$ 100,000,000
Sale of stock (in shares)		0	345,578
AS Ajax E II LLC
Class of Stock [Line Items]
Ownership percentage by parent (as percent)		53.10%		53.10%
2017-D
Class of Stock [Line Items]
Ownership percentage by parent (as percent)		50.00%		50.00%
Great Ajax II REIT
Class of Stock [Line Items]
Ownership percentage by parent (as percent)		99.90%		99.90%
Thetis Asset Management LLC
Class of Stock [Line Items]
Treasury stock, common (in shares)		(148,834)		(148,834)
Gregory
Class of Stock [Line Items]
Treasury stock, common (in shares)		(361,912)		(361,912)
Preferred stock
Class of Stock [Line Items]
Preferred stock discount | $		$ 0	$ 0		$ 8,200,000
Common stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		36,992,019	23,509,446	27,460,161	23,130,956
Exchange of shares (in shares)		9,464,524
Preferred stock, shares exchanged, shares issued and to be issued (in shares)		12,046,218
Issuance of shares under dividend reinvestment plan (in shares)		0	0
Common stock | Subsequent event
Class of Stock [Line Items]
Exchange of shares (in shares)	2,581,694
7.25% Series A preferred stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		135,930		424,949		2,307,400
Preferred stock, fixed-to-floating rate cumulative redeemable		7.25%		7.25%	7.25%	7.25%
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares		$ 25.00		$ 25.00		$ 25.00
Preferred stock, shares outstanding (in shares)		0		424,949
7.25% Series A preferred stock | Preferred stock
Class of Stock [Line Items]
Stock repurchased and retired during period, shares (in shares)					1,882,451
Exchange of shares (in shares)		424,949
Preferred stock, shares outstanding (in shares)		0	424,949	424,949	424,949
5.00% Series B preferred stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		363,245		1,135,590		2,892,600
Preferred stock, fixed-to-floating rate cumulative redeemable		5.00%		5.00%	5.00%	5.00%
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares		$ 25.00		$ 25.00		$ 25.00
Preferred stock, discount (in percent)					2.50%
Preferred stock, shares outstanding (in shares)		0		1,135,590
5.00% Series B preferred stock | Preferred stock
Class of Stock [Line Items]
Stock repurchased and retired during period, shares (in shares)					1,757,010
Stock repurchased and retired during period | $					$ 88,700,000
Stock repurchased and retired during period, average price per share (in dollars per share) | $ / shares					$ 24.37
Exchange of shares (in shares)		1,135,590
Preferred stock, shares outstanding (in shares)		0	1,135,590	1,135,590	1,135,590
At-the-Market Program
Class of Stock [Line Items]
Sale of common stock, net of offering costs | $			$ 2,400,000