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Fair Value of Financial Instruments - Fair Value Methodology (Details) - Residential whole loans $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential whole loans, fair value	$ 7,684,865	$ 7,511,210
UPB	9,018,124	9,194,832
Marked to Market Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential whole loans, fair value	44,300	44,900
UPB	76,300	78,200
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential whole loans, fair value	7,632,928	7,459,137
Level 3 | Discounted Cash Flow and Liquidation Model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential whole loans, fair value	7,588,625	7,414,218
Level 3 | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential whole loans, fair value	$ 7,276,067	$ 7,070,535
Level 3 | Discounted cash flow | Discount rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.067	0.076
Level 3 | Discounted cash flow | Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.057	0.062
Level 3 | Discounted cash flow | Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.200	0.200
Level 3 | Discounted cash flow | Prepayment rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.170	0.137
Level 3 | Discounted cash flow | Prepayment rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0	0
Level 3 | Discounted cash flow | Prepayment rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.510	0.583
Level 3 | Discounted cash flow | Default rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.017	0.018
Level 3 | Discounted cash flow | Default rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0	0
Level 3 | Discounted cash flow | Default rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.688	0.543
Level 3 | Discounted cash flow | Loss severity | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.117	0.123
Level 3 | Discounted cash flow | Loss severity | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0	0
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
Level 3 | Liquidation model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential whole loans, fair value	$ 312,558	$ 343,683
Level 3 | Liquidation model | Discount rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.087	0.088
Level 3 | Liquidation model | Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.080	0.080
Level 3 | Liquidation model | Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.200	0.200
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	2.40%	3.20%
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	(2.60%)	0.00%
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	9.30%	9.70%
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 9 months 18 days	1 year 8 months 12 days
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)	9 months 18 days	1 month 6 days
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
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	$ 697	$ 618
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	19	21
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	$ 10,000	$ 8,500

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The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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