Transactions with Related Parties - Summary of Expenses (Detail) - PNMAC Capital Management LLC [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Related Party Transaction [Line Items]
Expenses incurred on the Company’s behalf, net	$ 489	$ (514)	$ 1,059	$ 59
Common overhead incurred by PCM and its affiliates	1,276	1,176	2,512	2,177
Compensation	120	120	240	240
Total expenses incurred in transaction with affiliates	1,885	782	3,811	2,476
Payments and settlements during the period	$ 28,031	$ 15,957	$ 43,220	$ 23,615