Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024
Assets:
Short-term investment at fair value	$ 62,228		$ 420,553
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	774,021		825,865
Loans held for sale	7,490,473		8,217,468
Derivative assets:
Derivative asset, before netting	238,541		232,293
Netting	(38,238)		(119,217)
Total derivative assets	200,303		113,076
Investment in PennyMac Mortgage Investment Trust	920		944
Derivative liabilities:
Derivative liability, before netting	91,657		102,881
Netting	(74,478)		(61,981)
Net amounts of liabilities presented in the consolidated balance sheet	17,179		40,900
Derivative liabilities to PennyMac Mortgage Investment Trust	7,097
Mortgage servicing liabilities	1,593		1,683
PennyMac Mortgage Investment Trust
Derivative assets:
Total derivative assets	1,779
Principal-Only-Strip MBS
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	774,021	$ 784,958	825,865	$ 960,267	$ 914,223
Recurring basis
Assets:
Short-term investment at fair value	62,228		420,553
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	774,021		825,865
Loans held for sale	7,490,473		8,217,468
Derivative assets:
Derivative asset, before netting	238,541		232,293
Netting	(38,238)		(119,217)
Total derivative assets	200,303		113,076
Mortgage servicing rights			8,744,528
Total assets	18,183,666		18,322,434
Derivative liabilities:
Derivative liability, before netting	91,657		102,881
Netting	(74,478)		(61,981)
Net amounts of liabilities presented in the consolidated balance sheet	17,179		40,900
Mortgage servicing liabilities	1,593		1,683
Total liabilities	25,869		42,583
Recurring basis | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	2,313
Netting	(534)
Total derivative assets	1,779
Mortgage servicing rights	9,653,942
Investment in PennyMac Mortgage Investment Trust	920		944
Derivative liabilities:
Derivative liability, before netting	7,631
Netting	(534)
Total liabilities	7,097
Recurring basis | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	132,413		56,946
Derivative liabilities:
Derivative liability, before netting	5,334		23,381
Recurring basis | Interest rate lock commitments | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	1,608
Derivative liabilities:
Derivative liability, before netting	7,097
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	36,077		3,701
Derivative liabilities:
Derivative liability, before netting	19,548		66,646
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	43,557		152,526
Derivative liabilities:
Derivative liability, before netting	66,775		12,854
Recurring basis | Forward contracts | Sales | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	705
Derivative liabilities:
Derivative liability, before netting	534
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting			3,278
Recurring basis | Total return swap
Derivative assets:
Derivative asset, before netting	105
Recurring basis | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	15,431		3,250
Recurring basis | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	10,958		12,592
Recurring basis | Level 1
Assets:
Short-term investment at fair value	62,228		420,553
Derivative assets:
Derivative asset, before netting	26,389		15,842
Total derivative assets	26,389		15,842
Total assets	89,537		437,339
Recurring basis | Level 1 | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	920		944
Recurring basis | Level 1 | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	15,431		3,250
Recurring basis | Level 1 | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	10,958		12,592
Recurring basis | Level 2
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	774,021		825,865
Loans held for sale	7,037,572		7,783,415
Derivative assets:
Derivative asset, before netting	79,739		159,505
Total derivative assets	79,739		159,505
Total assets	7,892,037		8,768,785
Derivative liabilities:
Derivative liability, before netting	86,323		79,500
Net amounts of liabilities presented in the consolidated balance sheet	86,323		79,500
Total liabilities	86,857		79,500
Recurring basis | Level 2 | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	705
Total derivative assets	705
Derivative liabilities:
Derivative liability, before netting	534
Total liabilities	534
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	36,077		3,701
Derivative liabilities:
Derivative liability, before netting	19,548		66,646
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	43,557		152,526
Derivative liabilities:
Derivative liability, before netting	66,775		12,854
Recurring basis | Level 2 | Forward contracts | Sales | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	705
Derivative liabilities:
Derivative liability, before netting	534
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting			3,278
Recurring basis | Level 2 | Total return swap
Derivative assets:
Derivative asset, before netting	105
Recurring basis | Level 3
Assets:
Loans held for sale	452,901		434,053
Derivative assets:
Derivative asset, before netting	132,413		56,946
Total derivative assets	132,413		56,946
Mortgage servicing rights			8,744,528
Total assets	10,240,864		9,235,527
Derivative liabilities:
Derivative liability, before netting	5,334		23,381
Net amounts of liabilities presented in the consolidated balance sheet	5,334		23,381
Mortgage servicing liabilities	1,593		1,683
Total liabilities	14,024		25,064
Recurring basis | Level 3 | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	1,608
Total derivative assets	1,608
Mortgage servicing rights	9,653,942
Derivative liabilities:
Derivative liability, before netting	7,097
Total liabilities	7,097
Recurring basis | Level 3 | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	132,413		56,946
Derivative liabilities:
Derivative liability, before netting	5,334		$ 23,381
Recurring basis | Level 3 | Interest rate lock commitments | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Derivative asset, before netting	1,608
Derivative liabilities:
Derivative liability, before netting	$ 7,097