Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 04, 2020
Entity Information [Line Items]
Document Transition Report	false
Entity Registrant Name	GREAT AJAX CORP.
Document Period End Date	Mar. 31, 2020
Entity Central Index Key	0001614806
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Current Reporting Status	Yes
Document Type	10-Q
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
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
Entity File Number	001-36844
Entity Tax Identification Number	47-1271842
City Area Code	503
Local Phone Number	505-5670
Entity Incorporation, State or Country Code	MD
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		22,921,935
Document Quarterly Report	true
AJXA
Entity Information [Line Items]
Trading Symbol	AJXA
Security Exchange Name	NYSE
Title of 12(g) Security	7.25% Convertible Senior Notes due 2024
Common Stock
Entity Information [Line Items]
Trading Symbol	AJX
Security Exchange Name	NYSE
Title of 12(g) Security	Common stock, par value $0.01 per share