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Related party Transactions - Narrative (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) calender	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)
Related Party Transaction [Line Items]
Available-for-sale Securities, Gross Realized Gains				$ 200
Payments to Acquire Debt Securities, Available-for-sale			$ 187,825	176,363	$ 0
Investments at fair value			231,685	146,811
Investments in beneficial interests			57,954	22,086
Amount of transaction			17,013	14,587
Management fee payable			1,634	881
Incentive Fee Expense			$ 700	100	0
Period of termination of license agreement			30 days
Gain on sale of mortgage loans			$ 7,123	0	$ 0
Investment In Securities			187,800	175,300
Sale of mortgage loans			180,992
Oileus Residential Loan Trust
Related Party Transaction [Line Items]
Investment in debt securities						$ 6,300
Available-for-sale Securities, Gross Realized Gains				200
2018-C
Related Party Transaction [Line Items]
Aggregate unpaid principal balance of mortgage loans on real estate	$ 50,100	$ 52,800
Payments to Acquire Debt Securities, Available-for-sale	$ 45,100	$ 47,400
Gregory
Related Party Transaction [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 12,000
Fixed interest rate			7.20%
Ajax Mortgage Loan Trust 2019-C
Related Party Transaction [Line Items]
Percentage of ownership interests in joint venture			34.00%
Investment In Securities			$ 12,100
Sale of mortgage loans			$ 176,900
Management Agreement \| Thetis
Related Party Transaction [Line Items]
Base management fee percentage			1.50%
Amended And Restated Management Agreement \| Thetis
Related Party Transaction [Line Items]
Management fee payable			$ 1,000
Percentage of base management fees payable in cash			75.00%
Percentage of base management fee payable in shares of common stock			25.00%
Percentage in excess of base management fees payable in cash			50.00%
Percentage in excess of base management fees payable in shares			50.00%
Period of common shares held as base management fee (at least)			3 years
Percentage of remaining incentive fee payable in common stock			20.00%
Percentage of remaining incentive fee in excess of book value			8.00%
Number of calender quarters \| calender			8
Percentage of remaining incentive fee payable in cash			80.00%
Fraction of independent directors			66.67%
Servicing Agreement \| Gregory
Related Party Transaction [Line Items]
Servicing fees percentage			0.42%
Servicing Agreement \| Gregory \| Minimum
Related Party Transaction [Line Items]
Servicing fees percentage			0.65%
Servicing Agreement \| Gregory \| Maximum
Related Party Transaction [Line Items]
Servicing fees percentage			1.25%
Prepaid Expenses and Other Current Assets [Member]
Related Party Transaction [Line Items]
Amount of transaction			$ 241	4
Prepaid Expenses and Other Current Assets [Member] \| Gregory
Related Party Transaction [Line Items]
Amount of transaction			687	11
Prepaid Expenses and Other Current Assets [Member] \| Gregory \| Receivable from Servicer for REO acquisitions
Related Party Transaction [Line Items]
Amount of transaction			585
Prepaid Expenses and Other Current Assets [Member] \| Thetis
Related Party Transaction [Line Items]
Amount of transaction			87
Beneficial interests in securitization trusts
Related Party Transaction [Line Items]
Investments in beneficial interests			31,400	21,800
Beneficial interests in securitization trusts \| Ajax Mortgage Loan Trust 2019-C
Related Party Transaction [Line Items]
Investments in beneficial interests			8,000
Senior Notes
Related Party Transaction [Line Items]
Investments at fair value			139,600	144,100
Subordinated Debt [Member]
Related Party Transaction [Line Items]
Investments at fair value			$ 16,800	$ 9,400