Related Party Transactions - Narrative (Details)				1 Months Ended		3 Months Ended		12 Months Ended			27 Months Ended
		Jan. 31, 2023 USD ($)	Nov. 22, 2019 USD ($)	Feb. 28, 2023 USD ($) residential_rpl	Jan. 31, 2022 USD ($)	Mar. 31, 2024 USD ($) loanPool loan calendarQuarter	Mar. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($)	Dec. 31, 2020 USD ($) loanPool	Dec. 31, 2019 USD ($) loanPool	Jan. 31, 2022 USD ($) privateCapitalRaise shares	Dec. 31, 2023 USD ($) loanPool	Nov. 30, 2023 USD ($)
Related Party Transaction [Line Items]
Investments in securities held-to-maturity	[1]					$ 54,085,000						$ 59,691,000
Investment in equity method investments						0	$ 726,000
Impairment loss of beneficial interest							$ (1,000,000)
Note and interest outstanding						4,240,000						$ 7,307,000
Number of private capital raises | privateCapitalRaise											2
Proceeds from issuance of private placement									$ 125,000,000
Unpaid principal balance						$ 58,900,000
Period of termination of license agreement (in days)						30 days
Residential RPLs
Related Party Transaction [Line Items]
Number of mortgage loans on real estate				1		0	3
Purchase price				$ 200,000
Unpaid principal balance				200,000			$ 800,000
Collateral value				$ 400,000
Management fee (including management termination fee)
Related Party Transaction [Line Items]
Incentive fee payable						$ 0	0
Legacy entities
Related Party Transaction [Line Items]
Cash payment in business acquisition										$ 1,000,000
Gaea Real Estate Corp.
Related Party Transaction [Line Items]
Ownership percentage (in percent)						22.20%						22.20%
Proceeds from issuance of private placement			$ 66,300,000		$ 30,000,000						$ 96,300,000
Private placement share issuance (in shares) | shares											6,247,794
Investments In affiliates					$ 25,500,000						$ 25,500,000
Private capital raise, number common stock and warrants issued (in shares) | shares											1,704,436
Equity method investment, common stock and warrants acquired (in shares) | shares											371,103
Gaea Real Estate Corp. | Third party
Related Party Transaction [Line Items]
Ownership percentage by third parties (in percent)						77.80%						77.80%
AS Ajax E LLC
Related Party Transaction [Line Items]
Ownership percentage (in percent)						16.50%						16.50%
Investment in Ajax E Master Trust | AS Ajax E LLC
Related Party Transaction [Line Items]
Ownership interest in real estate trust (in percent)						5.00%						5.00%
Loan pool LLCs
Related Party Transaction [Line Items]
Ownership percentage (in percent)						40.00%				40.40%		40.00%
Number of entities | loanPool						1				3		1
Number of entities that sold assets | loanPool									1
Payments to acquire finance receivables								$ 300,000
Unpaid principal balance								$ 400,000
Servicer
Related Party Transaction [Line Items]
Investment in equity method investments		$ 700,000
Ownership percentage (in percent)						9.70%						9.70%
Investments in securities
Related Party Transaction [Line Items]
Fair value						$ 125,100,000						$ 131,600,000
Investment in beneficial interests
Related Party Transaction [Line Items]
Fair value						67,439,000						81,316,000
Beneficial interest, carrying amount						88,600,000						104,200,000
Senior notes
Related Party Transaction [Line Items]
Debt securities, realized loss						$ 0	$ (3,000,000)
Thetis Asset Management LLC | Management agreement
Related Party Transaction [Line Items]
Percentage of base management fee (in percent)						1.50%
Thetis Asset Management LLC | Amended and restated management agreement
Related Party Transaction [Line Items]
Percentage in excess of base management fees payable in shares (in percent)						50.00%
Percentage of management fees payable in cash, minimum (in percent)						50.00%
Percentage of management fees payable in cash, maximum (in percent)						100.00%
Period of common shares held as base management fee (at least) (in years)						3 years
Percentage of remaining incentive fee in excess of book value (in percent)						8.00%
Number of calendar quarters | calendarQuarter						8
Percentage of remaining incentive fee payable in shares (in percent)						20.00%
Percentage of remaining incentive fee payable in cash (in percent)						80.00%
Percentage of independent directors (in percent)						66.67%
Gregory
Related Party Transaction [Line Items]
Maximum borrowing capacity						$ 12,000,000							$ 3,500,000
Fixed interest rate (in percent)													3.00%
Gregory | Related Party
Related Party Transaction [Line Items]
Due from related parties						10,900,000						9,300,000
Note and interest outstanding						$ 1,800,000						$ 3,300,000
Gregory | Servicing agreement
Related Party Transaction [Line Items]
Percentage of fair market value of REO (in percent)						1.00%
Percentage of purchase price of REO (in percent)						1.00%
Gregory | Servicing agreement | Minimum
Related Party Transaction [Line Items]
Servicing fees (in percent)						0.65%
Gregory | Servicing agreement | Maximum
Related Party Transaction [Line Items]
Servicing fees (in percent)						1.25%

[1] On January 1, 2023, the Company transferred certain of its investments in securities to held-to-maturity ("HTM") due to European risk retention regulations. As of March 31, 2024, Investments in securities HTM includes an allowance for expected credit losses of zero and remaining discount of $5.2 million related to the unamortized unrealized loss in Accumulated other comprehensive income ("AOCI"). As of December 31, 2023, Investments in securities HTM includes an allowance for expected credit losses of zero and remaining discount of $6.0 million related to the unamortized unrealized loss in AOCI.