Debt - Schedule of Securitization Notes Outstanding (Details) - Mortgage loans - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Deferred issuance costs	$ (7.0)	$ (6.3)
Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Ownership percentage	100.00%
Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Ownership percentage	100.00%
Class A notes | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 115.8
Interest rate	3.16%
Class A notes | Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Original Principal	$ 130.2
Interest rate	3.75%
Class A notes | Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 177.8	139.0
Interest rate	3.75%
Ownership percentage	50.00%
Class A notes | Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Original Principal	$ 170.5
Interest rate	4.36%
Class B Notes | Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Original Principal	$ 15.9	$ 15.9
Interest rate	5.25%
Class B 1 Notes | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 9.0
Interest rate	3.75%
Class B 1 Notes | Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Original Principal	$ 13.0
Interest rate	5.25%
Class B 1 Notes | Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Ownership percentage	50.00%
Class B 1 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 7.5
Interest rate	3.50%
Class B 1 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 11.5
Interest rate	3.50%
Class B 2 Notes | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 7.5
Interest rate	3.75%
Class B 2 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 7.1
Class B 2 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	10.4
Trust Certificate | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original principal, trust certificates	$ 14.3
Interest rate	0.00%
Trust Certificate | Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Original principal, trust certificates	$ 42.8
Interest rate	0.00%
Trust Certificate | Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Original principal, trust certificates	$ 40.9
Interest rate	0.00%
Deferred issuance costs | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Interest rate	0.00%
Deferred issuance costs	$ (1.8)
Deferred issuance costs | Ajax Mortgage Loan Trust 2017-C/ November 2017
Debt Instrument [Line Items]
Interest rate	0.00%
Deferred issuance costs	$ (1.7)
Deferred issuance costs | Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Interest rate	0.00%
Deferred issuance costs	$ (1.1)
Deferred issuance costs | Ajax Mortgage Loan Trust 2018-C/ September 2018
Debt Instrument [Line Items]
Interest rate	0.00%
Deferred issuance costs	$ (2.0)
Deferred issuance costs | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Interest rate	0.00%
Deferred issuance costs	$ (2.7)
Deferred issuance costs | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Interest rate	0.00%
Deferred issuance costs	$ (1.8)
Class M1 Notes | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 9.7
Interest rate	3.50%
Class M1 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 9.3
Interest rate	3.50%
Class M1 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 6.1
Interest rate	3.50%
Class M2 Notes | Ajax Mortgage Loan Trust 2017-B/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 9.5
Interest rate	3.50%
Class B Certificates | Ajax Mortgage Loan Trust 2017-D/ December 2017
Debt Instrument [Line Items]
Original Principal	$ 44.5
Interest rate	0.00%
Ownership percentage	50.00%
Class A-1 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 140.4
Interest rate	2.96%
Class A-1 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 110.1
Interest rate	2.86%
Class A-2 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 6.1
Interest rate	3.50%
Class A-2 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 12.5
Interest rate	3.50%
Class A-3 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 10.1
Interest rate	3.50%
Class A-3 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 5.1
Interest rate	3.50%
Class B-3 Notes | Ajax Mortgage Loan Trust 2019 D July 2019
Debt Instrument [Line Items]
Original Principal	$ 12.8
Class B-3 Notes | Ajax Mortgage Loan Trust 2019 F November 2019
Debt Instrument [Line Items]
Original Principal	$ 15.1