Subsequent Events - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 05, 2021 USD ($) transaction residentialRPL loanPool seller residentialNPL	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan	Nov. 04, 2021 $ / shares
Subsequent Event [Line Items]
Estimated market value of the underlying collateral					$ 44.2
Subsequent event
Subsequent Event [Line Items]
Dividends payable, amount per share (in dollars per share) | $ / shares						$ 0.24
Residential RPLs
Subsequent Event [Line Items]
Number of mortgage loans on real estate | loan		4	244	241	270
Aggregate unpaid principal balance of mortgage loans on real estate		$ 0.5	$ 46.3	$ 41.7	$ 48.2
Residential RPLs | Two sellers | Subsequent event
Subsequent Event [Line Items]
Number of mortgage loans on real estate | residentialRPL	20
Aggregate unpaid principal balance of mortgage loans on real estate	$ 2.4
Number of transaction | transaction	2
Number of sellers | seller	2
Percentage of unpaid principal balance of loan acquired	68.80%
Percentage of estimated market value of the underlying collateral	47.30%
Estimated market value of the underlying collateral	$ 3.5
Residential RPLs | four sellers | Subsequent event
Subsequent Event [Line Items]
Number of mortgage loans on real estate | residentialRPL	4
Aggregate unpaid principal balance of mortgage loans on real estate	$ 1.7
Number of transaction | transaction	4
Percentage of unpaid principal balance of loan acquired	96.50%
Percentage of estimated market value of the underlying collateral	70.30%
Estimated market value of the underlying collateral	$ 2.4
Residential NPLs
Subsequent Event [Line Items]
Number of mortgage loans on real estate | loan		364	1	367	2
Aggregate unpaid principal balance of mortgage loans on real estate		$ 90.9	$ 0.5	$ 91.5	$ 0.7
Residential NPLs | Subsequent event | Various non-consolidated joint ventures
Subsequent Event [Line Items]
Number of mortgage loans on real estate | loanPool	2,498
Aggregate unpaid principal balance of mortgage loans on real estate	$ 350.9
Number of transaction | transaction	1
Percentage of unpaid principal balance of loan acquired	103.50%
Percentage of estimated market value of the underlying collateral	49.40%
Estimated market value of the underlying collateral	$ 734.9
Investment ownership percentage	16.30%
Residential NPLs | Two sellers | Subsequent event
Subsequent Event [Line Items]
Number of mortgage loans on real estate | residentialNPL	3
Aggregate unpaid principal balance of mortgage loans on real estate	$ 0.8
Number of transaction | transaction	2
Percentage of unpaid principal balance of loan acquired	93.90%
Percentage of estimated market value of the underlying collateral	61.80%
Estimated market value of the underlying collateral	$ 1.2
Residential NPLs | One seller | Subsequent event
Subsequent Event [Line Items]
Number of mortgage loans on real estate | loanPool	1
Aggregate unpaid principal balance of mortgage loans on real estate	$ 0.4
Number of transaction | transaction	1
Percentage of unpaid principal balance of loan acquired	97.40%
Percentage of estimated market value of the underlying collateral	84.40%
Estimated market value of the underlying collateral	$ 0.4