Cover - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 02, 2020	Jun. 30, 2019
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-36844
Entity Registrant Name	GREAT AJAX CORP
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	47-1271842
Entity Address, Address Line One	9400 SW Beaverton-Hillsdale Hwy,
Entity Address, Address Line Two	Suite 131
Entity Address, City or Town	Beaverton
Entity Address, State or Province	OR
Entity Address, Postal Zip Code	97005
City Area Code	503
Local Phone Number	505-5670
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 258,529,624
Entity Common Stock, Shares Outstanding (in shares)		22,142,143
Documents Incorporated by Reference	Portions of the registrant’s Definitive Proxy Statement with respect to its 2019 Annual Meeting of Stockholders are incorporated by reference into this Annual Report on Form 10-K in response to Part III, Items 10, 11, 12, 13 and 14.
Entity Central Index Key	0001614806
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common stock, par value $0.01 per share
Security Exchange Name	NYSE
Trading Symbol	AJX
7.25% Convertible Senior Notes due 2024
Entity Information [Line Items]
Title of 12(b) Security	7.25% Convertible Senior Notes due 2024
Security Exchange Name	NYSE
Trading Symbol	AJXA