Fair Value of Financial Instruments - Fair Value Methodology (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Nonperforming
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchased performing loans, fair value	$ 699,311	$ 795,894
Purchases excluded from level 2 fair value	499	215
Nonperforming | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchased performing loans, fair value	512,213	546,675
Nonperforming | Liquidation model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchased performing loans, fair value	187,098	249,219
Simple average amount	$ 498	$ 457
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Discount rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.076	0.070
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.071	0.063
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.111	0.100
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Prepayment rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.066	0.089
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Prepayment rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.000	0.000
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Prepayment rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.282	0.335
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Default rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.027	0.037
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Default rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.000	0.000
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Default rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.389	0.524
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Loss severity | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.098	0.113
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Loss severity | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.000	0.000
Nonperforming | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Loss severity | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	1.000	1.000
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Discount rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.078
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.078
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.078
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Annual change in home prices | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Annual change in home prices	3.30%	6.90%
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Annual change in home prices | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Annual change in home prices	(0.20%)	(5.40%)
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Annual change in home prices | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Annual change in home prices	12.60%	59.70%
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Liquidation timeline (in years) | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation timeline (in years)	2 years	1 year 10 months 24 days
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Liquidation timeline (in years) | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation timeline (in years)	1 month 6 days	1 month 6 days
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Liquidation timeline (in years) | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation timeline (in years)	4 years 6 months	4 years 6 months
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Current value of underlying properties | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current value of underlying properties	$ 843	$ 743
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Current value of underlying properties | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current value of underlying properties	43	28
Nonperforming | Residential whole loans, at fair value | Level 3 | Liquidation model | Current value of underlying properties | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current value of underlying properties	4,720	4,000
Performing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchased performing loans, fair value	6,093,612	4,880,321
Performing | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchased performing loans, fair value	5,996,971	4,857,587
Performing | Liquidation model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchased performing loans, fair value	$ 96,641	$ 22,734
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Discount rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.084	0.076
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.065	0.056
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.248	0.227
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Prepayment rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.076	0.079
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Prepayment rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.000	0.000
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Prepayment rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.433	0.448
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Default rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.005	0.008
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Default rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.000	0.000
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Default rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.270	0.194
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Loss severity | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.108	0.073
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Loss severity | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.000	0.000
Performing | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Loss severity | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.984	1.000
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Discount rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.078
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.078
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.078
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Annual change in home prices | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Annual change in home prices	2.30%	3.20%
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Annual change in home prices | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Annual change in home prices	0.00%	(1.00%)
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Annual change in home prices | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Annual change in home prices	9.80%	10.70%
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Liquidation timeline (in years) | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation timeline (in years)	1 year 7 months 6 days	1 year 10 months 24 days
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Liquidation timeline (in years) | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation timeline (in years)	1 month 6 days	9 months 18 days
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Liquidation timeline (in years) | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation timeline (in years)	4 years	4 years 2 months 12 days
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Current value of underlying properties | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current value of underlying properties	$ 1,567	$ 1,319
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Current value of underlying properties | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current value of underlying properties	40	50
Performing | Residential whole loans, at fair value | Level 3 | Liquidation model | Current value of underlying properties | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current value of underlying properties	$ 5,500	$ 2,850