Transactions with Related Parties - Summary of Management Fee Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Related Party Transaction [Line Items]
Total management fee incurred during the period	$ 7,133	$ 7,078	$ 14,321	$ 14,335
PNMAC Capital Management LLC [Member]
Related Party Transaction [Line Items]
Total management fee incurred during the period	7,133	7,078	14,321	14,335
Average shareholders' equity amounts used to calculate base management fee expense	1,912,522	1,892,505	1,919,962	1,927,305
PNMAC Capital Management LLC [Member] | Base [Member]
Related Party Transaction [Line Items]
Total management fee incurred during the period	7,133	7,078	14,321	14,335
PNMAC Capital Management LLC [Member] | Performance incentive [Member]
Related Party Transaction [Line Items]
Total management fee incurred during the period	$ 0	$ 0	$ 0	$ 0