Schedule IV Mortgage loans on real estate - Schedule of Mortgage Loans (Details)		12 Months Ended
		Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		6,184	7,111
Carrying value	[1],[2]	$ 1,151,469,000	$ 1,310,873,000
Principal amount subject to delinquent principal and interest		532,820,000
Amount of balloon payments at maturity		148,887,000
Aggregate cost for federal income tax purposes		1,067,300,000
Maximum
Mortgage Loans on Real Estate [Line Items]
Principal amount subject to delinquent principal and interest		$ 5,000,000.0
$0 – 49,999
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		598
Carrying value		$ 16,516,000
Principal amount subject to delinquent principal and interest		8,438,000
Amount of balloon payments at maturity		$ 1,452,000
$0 – 49,999 | Minimum
Mortgage Loans on Real Estate [Line Items]
Interest rate		0.00%
$0 – 49,999 | Maximum
Mortgage Loans on Real Estate [Line Items]
Interest rate		13.50%
$50,000 – 99,999
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		1,185
Carrying value		$ 84,471,000
Principal amount subject to delinquent principal and interest		40,491,000
Amount of balloon payments at maturity		$ 6,359,000
$50,000 – 99,999 | Minimum
Mortgage Loans on Real Estate [Line Items]
Interest rate		0.00%
$50,000 – 99,999 | Maximum
Mortgage Loans on Real Estate [Line Items]
Interest rate		15.00%
$100,000 – 149,999
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		1,294
Carrying value		$ 147,677,000
Principal amount subject to delinquent principal and interest		75,703,000
Amount of balloon payments at maturity		$ 10,714,000
$100,000 – 149,999 | Minimum
Mortgage Loans on Real Estate [Line Items]
Interest rate		0.00%
$100,000 – 149,999 | Maximum
Mortgage Loans on Real Estate [Line Items]
Interest rate		17.00%
$150,000 – 199,999
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		889
Carrying value		$ 139,959,000
Principal amount subject to delinquent principal and interest		69,309,000
Amount of balloon payments at maturity		$ 9,425,000
$150,000 – 199,999 | Minimum
Mortgage Loans on Real Estate [Line Items]
Interest rate		2.00%
$150,000 – 199,999 | Maximum
Mortgage Loans on Real Estate [Line Items]
Interest rate		13.00%
$200,000 – 249,999
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		584
Carrying value		$ 118,735,000
Principal amount subject to delinquent principal and interest		59,263,000
Amount of balloon payments at maturity		$ 11,657,000
$200,000 – 249,999 | Minimum
Mortgage Loans on Real Estate [Line Items]
Interest rate		1.99%
$200,000 – 249,999 | Maximum
Mortgage Loans on Real Estate [Line Items]
Interest rate		10.93%
$250,000+
Mortgage Loans on Real Estate [Line Items]
Loan Count | loan		1,634
Carrying value		$ 644,111,000
Principal amount subject to delinquent principal and interest		279,616,000
Amount of balloon payments at maturity		$ 109,280,000
$250,000+ | Minimum
Mortgage Loans on Real Estate [Line Items]
Interest rate		0.00%
$250,000+ | Maximum
Mortgage Loans on Real Estate [Line Items]
Interest rate		12.00%

[1] As of December 31, 2019, balances for Mortgage loans, net includes $341.8 million and Secured borrowings, net of deferred costs includes $284.8 million from the 50.0% and 63.0% owned joint ventures, respectively. As of December 31, 2018, balances for Mortgage loans, net include $377.0 million and Secured borrowings, net of deferred costs includes $231.9 million from the 50.0% and 63.0% owned joint ventures, all of which the Company consolidates under U.S. Generally Accepted Accounting Principles ("U.S. GAAP").

[2] Mortgage loans, net include $908.6 million and $897.8 million of loans at December 31, 2019 and December 31, 2018, respectively, transferred to securitization trusts that are variable interest entities (“VIEs”); these loans can only be used to settle obligations of the VIEs. Secured borrowings consist of notes issued by VIEs that can only be settled with the assets and cash flows of the VIEs. The creditors do not have recourse to the primary beneficiary (Great Ajax Corp.). See Note 9 — Debt. Mortgage loans, net include $2.0 million and $1.2 million of allowance for loan losses at December 31, 2019 and December 31, 2018, respectively.