Other Assets and Liabilities - Summary of Components of Other Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, Other Assets and Other Liabilities Disclosure [Abstract]
Accrued interest receivable	$ 189,609	$ 189,569
Derivative assets	114,558	7,349
Loan portfolio payments held by servicer	63,566	68,489
Accounts receivable and other assets	1,595	1,318
Prepaid expenses	118	1,067
Collateral deposited under derivative agreements	0	103,110
Total	$ 369,446	$ 370,902