Number of non controlling interest subsidiaries

No definition available.

Name:	ajx_NumberOfNonControllingInterestSubsidiaries
Namespace Prefix:	ajx_
Data Type:	xbrli:integerItemType
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:	dtr-types: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_ClassOfStockLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21475-112644

+ Details

Name:	us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of warrants or rights outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Face amount or stated value per share of common stock.

+ References

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

+ References

+ Details

Name:	us-gaap_CommonStockSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

+ Details

Name:	us-gaap_CommonStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21463-112644

Reference 2: 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(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

+ Details

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ 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(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

+ Details

Name:	us-gaap_PreferredStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

+ References

+ Details

Name:	us-gaap_PreferredStockSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

+ References

+ Details

Name:	us-gaap_PreferredStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

+ References

+ Details

Name:	us-gaap_PreferredStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cash inflow from capital contributions to an entity associated with a dividend reinvestment plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the amount received from entity's raising of capital via private rather than public placement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfPrivatePlacement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

+ References

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

+ 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 210.5-02.29,30)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

+ Details

Name:	us-gaap_TreasuryStockShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_WarrantsAndRightsOutstandingTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_TransactionTypeAxis=ajx_OpenMarketPurchasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=ajx_AttheMarketProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_SeriesAPreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_SeriesBPreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ajx_ThetisAssetManagementLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ajx_ASAjaxEIILLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=ajx_ThirdPartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=ajx_GreatAjaxCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ajx_SecuritizationTrust2017DMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ajx_GreatAjaxIIREITMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ajx_SecuritizationTrust2018CMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Equity - Narrative (Details)		3 Months Ended			6 Months Ended
Equity - Narrative (Details)	Apr. 06, 2020 USD ($)	Jun. 30, 2021 USD ($) entity $ / shares shares	Mar. 31, 2021 shares	Jun. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2021 USD ($) entity $ / shares shares	Jun. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2020 entity $ / shares shares	Mar. 31, 2020 shares	Feb. 28, 2020 USD ($)	Dec. 31, 2019 shares	Dec. 31, 2018
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		22,993,246			22,993,246		22,978,339
Common stock, par value per share (in dollars per share) \| $ / shares		$ 0.01			$ 0.01		$ 0.01
Common stock, shares authorized (in shares)		125,000,000			125,000,000		125,000,000
Proceeds from issuance of preferred stock and warrants, net of offering costs \| $	$ 125,000,000.0			$ 130,000,000.0	$ 0	$ 124,977,000
Preferred stock, par value per share (in dollars per share) \| $ / shares		$ 0.01			$ 0.01		$ 0.01
Warrant term				5 years		5 years
Class of warrant or right, outstanding (in shares)		6,500,000		6,500,000	6,500,000	6,500,000
Investment warrants, exercise price (in dollars per share) \| $ / shares				$ 10.00		$ 10.00
Preferred stock, shares authorized (in shares)		25,000,000			25,000,000		25,000,000
Common stock authorized \| $									$ 25,000,000.0
Treasury stock (in shares)		126,609			126,609		107,243
Sale of common stock pursuant to dividend reinvestment plan \| $					$ 95,000	$ 41,000
Common stock, shares issued (in shares)		22,993,246			22,993,246		22,978,339
Number of non controlling interest subsidiaries \| entity		3			3		4
Open market purchases
Class of Stock [Line Items]
Treasury stock (in shares)		48,464			48,464		48,464
At-the-Market Program
Class of Stock [Line Items]
Common stock authorized \| $		$ 50,000,000.0			$ 50,000,000.0
Common stock, shares issued (in shares)		0		0	0	0
7.25% Series A preferred stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		2,307,400		2,307,400	2,307,400	2,307,400	2,307,400
Preferred stock, fixed-to-floating rate cumulative redeemable				7.25%	7.25%
Preferred stock, par value per share (in dollars per share) \| $ / shares				$ 25.00		$ 25.00
Preferred stock, shares outstanding (in shares)		2,307,400	2,307,400	2,307,400	2,307,400	2,307,400	2,307,400	0		0
Preferred stock - Series B shares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		2,892,600		2,892,600	2,892,600	2,892,600	2,892,600
Preferred stock, fixed-to-floating rate cumulative redeemable				5.00%	5.00%
Preferred stock, par value per share (in dollars per share) \| $ / shares				$ 25.00		$ 25.00
Preferred stock, shares outstanding (in shares)		2,892,600	2,892,600	2,892,600	2,892,600	2,892,600	2,892,600	0		0
Common stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)		22,993,246	22,988,847	22,924,982	22,993,246	22,924,982	22,978,339	22,921,935		22,142,143
Issuance of shares under dividend reinvestment plan (in shares)		3,820	4,228	5,057	8,048	5,057
Sale of common stock pursuant to dividend reinvestment plan \| $		$ 48,000		$ 41,000	$ 100,000	$ 41,000
Thetis Asset Management LLC
Class of Stock [Line Items]
Treasury stock (in shares)		78,145			78,145		58,779
Investment in AS Ajax E II LLC
Class of Stock [Line Items]
Percentage of ownership interests in joint venture		53.10%			53.10%		53.10%
Investment in AS Ajax E II LLC \| Third party
Class of Stock [Line Items]
Ownership percentage by third parties		46.90%			46.90%
Investment in AS Ajax E II LLC \| Great Ajax Corp
Class of Stock [Line Items]
Percentage of ownership interests in joint venture		53.10%			53.10%		53.10%
2017-D
Class of Stock [Line Items]
Percentage of ownership interests in joint venture		50.00%			50.00%
2017-D \| Great Ajax Corp
Class of Stock [Line Items]
Ownership percentage by parent		50.00%			50.00%		50.00%
Great Ajax II REIT \| Third party
Class of Stock [Line Items]
Ownership percentage by third parties		0.10%			0.10%		0.10%
Great Ajax II REIT \| Great Ajax Corp
Class of Stock [Line Items]
Ownership percentage by parent		99.90%			99.90%		99.90%
2018-C
Class of Stock [Line Items]
Percentage of ownership interests in joint venture		37.00%	37.00%		37.00%						37.00%
2018-C \| Third party
Class of Stock [Line Items]
Ownership percentage by third parties		0.00%			0.00%
Ownership percentage by parent							63.00%
2018-C \| Great Ajax Corp
Class of Stock [Line Items]
Ownership percentage by parent		100.00%			100.00%