Mortgage Loans - Narrative (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Mortgage Loans on Real Estate [Line Items]
Carrying value	[1],[2]	$ 1,151,469	$ 1,310,873
Investment Income, Interest		$ 95,100	$ 102,500	$ 89,900
Number of loans | loan		6,184	7,111
Interest income		$ 112,416	$ 108,181	91,424
Certain loans acquired in transfer not accounted for as debt securities, accretable yield, reclassifications (to) from nonaccretable difference		(33,200)	33,100
Provision for loan losses		(803)	(1,164)	0
Financing Receivable, Allowance for Credit Losses		2,000	1,164	$ 0	$ 0
Sale of mortgage loans		180,992
Ajax Mortgage Loan Trust 2019-C
Mortgage Loans on Real Estate [Line Items]
Sale of mortgage loans		176,900
Re-performing loans
Mortgage Loans on Real Estate [Line Items]
Certain loans acquired in transfer not accounted for as debt securities, accretable yield, reclassifications (to) from nonaccretable difference		(30,300)
Non-performing loans
Mortgage Loans on Real Estate [Line Items]
Carrying value		30,869	$ 36,323
Number of mortgage loans on real estate | loan			36
Certain loans acquired in transfer not accounted for as debt securities, accretable yield, reclassifications (to) from nonaccretable difference		2,900
RPLs
Mortgage Loans on Real Estate [Line Items]
Carrying value		$ 1,085,514	$ 1,242,207
Number of mortgage loans on real estate | loan		573	810
Aggregate unpaid principal balance of mortgage loans on real estate		$ 122,500	$ 175,500
Non-performing loans
Mortgage Loans on Real Estate [Line Items]
Number Of Pools Of Mortgage Loans | loan		5	3
Number of mortgage loans on real estate | loan		35
Aggregate unpaid principal balance of mortgage loans on real estate		$ 6,700	$ 6,000
Re-performing loans
Mortgage Loans on Real Estate [Line Items]
Certain loans acquired in transfer not accounted for as debt securities, accretable yield, reclassifications (to) from nonaccretable difference		30,273	(33,389)
SBC loan pools
Mortgage Loans on Real Estate [Line Items]
Carrying value		11,652	21,203
Aggregate unpaid principal balance of mortgage loans on real estate			6,400
SBC loans non-pooled
Mortgage Loans on Real Estate [Line Items]
Carrying value		23,434	$ 11,140
Aggregate unpaid principal balance of mortgage loans on real estate		$ 19,000
Number of loans | loan		22	8
Non-performing loans
Mortgage Loans on Real Estate [Line Items]
Certain loans acquired in transfer not accounted for as debt securities, accretable yield, reclassifications (to) from nonaccretable difference		$ 2,922	$ 270

[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.