Debt - Schedule of Securitization Notes Outstanding (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Percentage of ownership interests in joint venture	34.00%
Mortgage loans
Debt Instrument [Line Items]
Deferred issuance costs	$ (6,200,000)	$ (7,000,000.0)
Mortgage loans \| Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Percentage of ownership interests in joint venture	50.00%
Reflection of required consolidation	100.00%
Mortgage loans \| Class A Notes \| 2018-C
Debt Instrument [Line Items]
Original Principal	$ 142,000,000.0	148,500,000
Securities Borrowed, Liability	134,900,000	141,000,000.0
Mortgage loans \| Class A Notes \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 115,800,000
Interest Rate	3.16%
Mortgage loans \| Class A Notes \| Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Original Principal	$ 130,200,000
Interest Rate	3.75%
Mortgage loans \| Class A Notes \| Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 177,800,000
Interest Rate	3.75%
Ownership percentage	50.00%
Mortgage loans \| Class A Notes \| Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Original Principal	$ 170,500,000
Interest Rate	4.36%
Mortgage loans \| Class B Notes \| 2018-C
Debt Instrument [Line Items]
Original Principal	$ 15,900,000	15,900,000
Securities Borrowed, Liability	5,900,000	$ 5,900,000
Mortgage loans \| Class B Notes \| Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Original Principal	$ 15,900,000
Interest Rate	5.25%
Mortgage loans \| Class B 1 Notes \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 9,000,000.0
Interest Rate	3.75%
Mortgage loans \| Class B 1 Notes \| Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Original Principal	$ 13,000,000.0
Interest Rate	5.25%
Mortgage loans \| Class B 1 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 7,500,000
Interest Rate	3.50%
Mortgage loans \| Class B 1 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 11,500,000
Interest Rate	3.50%
Mortgage loans \| Class B 2 Notes \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 7,500,000
Interest Rate	3.75%
Mortgage loans \| Class B 2 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 7,100,000
Mortgage loans \| Class B 2 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	10,400,000
Mortgage loans \| Trust Certificate \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original principal, trust certificates	$ 14,300,000
Interest Rate	0.00%
Mortgage loans \| Trust Certificate \| Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Original principal, trust certificates	$ 42,800,000
Interest Rate	0.00%
Mortgage loans \| Trust Certificate \| Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Original principal, trust certificates	$ 40,900,000
Interest Rate	0.00%
Mortgage loans \| Deferred issuance costs \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Interest Rate	0.00%
Deferred issuance costs	$ (1,800,000)
Mortgage loans \| Deferred issuance costs \| Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Interest Rate	0.00%
Deferred issuance costs	$ (1,700,000)
Mortgage loans \| Deferred issuance costs \| Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Interest Rate	0.00%
Deferred issuance costs	$ (1,100,000)
Mortgage loans \| Deferred issuance costs \| Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Interest Rate	0.00%
Deferred issuance costs	$ (2,000,000.0)
Mortgage loans \| Deferred issuance costs \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Interest Rate	0.00%
Deferred issuance costs	$ (2,700,000)
Mortgage loans \| Deferred issuance costs \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Interest Rate	0.00%
Deferred issuance costs	$ (1,800,000)
Mortgage loans \| Class M1 Notes \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 9,700,000
Interest Rate	3.50%
Mortgage loans \| Class M1 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 9,300,000
Interest Rate	3.50%
Mortgage loans \| Class M1 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 6,100,000
Interest Rate	3.50%
Mortgage loans \| Class M2 Notes \| Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 9,500,000
Interest Rate	3.50%
Mortgage loans \| Class B Certificates \| Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Original principal, trust certificates	$ 44,500,000
Interest Rate	0.00%
Ownership percentage	50.00%
Mortgage loans \| Class A-1 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 140,400,000
Interest Rate	2.96%
Mortgage loans \| Class A-1 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 110,100,000
Interest Rate	2.86%
Mortgage loans \| Class A-2 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 6,100,000
Interest Rate	3.50%
Mortgage loans \| Class A-2 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 12,500,000
Interest Rate	3.50%
Mortgage loans \| Class A-3 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 10,100,000
Interest Rate	3.50%
Mortgage loans \| Class A-3 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 5,100,000
Interest Rate	3.50%
Mortgage loans \| Class B-3 Notes \| Ajax Mortgage Loan Trust 2019-D/ July 2019
Debt Instrument [Line Items]
Original Principal	$ 12,800,000
Mortgage loans \| Class B-3 Notes \| Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 15,100,000

Debt, Required Consolidation Percent

No definition available.

Name:	ajx_DebtRequiredConsolidationPercent
Namespace Prefix:	ajx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage Of Ownership Interests In Joint Venture

+ References

No definition available.

+ Details

Name:	ajx_PercentageOfOwnershipInterestsInJointVenture
Namespace Prefix:	ajx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

It represents the residual amount entitled to after all debts of the trust satisfied.

+ References

No definition available.

+ Details

Name:	ajx_TrustCertificate
Namespace Prefix:	ajx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of liability associated with securities borrowed from entities in exchange for collateral.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226003-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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Balance Type:	credit
Period Type:	instant