Fair Value - Carrying and Fair Values of Notes Payable Secured by Credit Risk Transfer and Mortgage Servicing Rights and Exchangeable Senior Notes (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Notes Payable Secured by Credit Risk Transfer and Mortgage Servicing Assets [Member] | Carrying Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes payable	$ 2,933,845	$ 2,910,605
Notes Payable Secured by Credit Risk Transfer and Mortgage Servicing Assets [Member] | Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes payable	2,942,231	2,904,678
Unsecured Senior Notes [Member] | Carrying Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes payable	813,838	600,458
Unsecured Senior Notes [Member] | Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes payable	$ 800,382	$ 580,090