Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Assets:
Short-term investment at fair value	$ 667,934	$ 10,268
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	960,267
Loans held for sale	6,565,704	4,420,691
Derivative assets:
Derivative asset, before netting	246,693	258,809
Netting	(56,081)	(79,730)
Total derivative assets	190,612	179,079
Investment in PennyMac Mortgage Investment Trust	1,070	1,121
Derivative liabilities:
Derivative liability, before netting	103,236	101,866
Netting	(61,765)	(48,591)
Net amounts of liabilities presented in the consolidated balance sheet	41,471	53,275
Mortgage servicing liabilities	1,718	1,805
Principal-Only-Strip MBS
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	960,267
Recurring basis
Assets:
Short-term investment at fair value	667,934	10,268
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	960,267
Loans held for sale	6,565,704	4,420,691
Derivative assets:
Derivative asset, before netting	246,693	258,809
Netting	(56,081)	(79,730)
Total derivative assets	190,612	179,079
Mortgage servicing rights	7,752,292	7,099,348
Total assets	16,137,879	11,710,507
Derivative liabilities:
Derivative liability, before netting	103,236	101,866
Netting	(61,765)	(48,591)
Net amounts of liabilities presented in the consolidated balance sheet	41,471	53,275
Mortgage servicing liabilities	1,718	1,805
Total liabilities	43,189	55,080
Recurring basis | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,070	1,121
Recurring basis | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	120,837	90,313
Derivative liabilities:
Derivative liability, before netting	2,222	720
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	10,878	78,448
Derivative liabilities:
Derivative liability, before netting	50,487	5,141
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	57,180	6,151
Derivative liabilities:
Derivative liability, before netting	36,855	92,796
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting	1,892	413
Recurring basis | MBS call options
Derivative assets:
Derivative asset, before netting		6,265
Recurring basis | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	35,109	66,176
Recurring basis | Call options on Eurodollar futures | Sales
Derivative liabilities:
Derivative liability, before netting	13,672	3,209
Recurring basis | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	20,797	11,043
Recurring basis | Level 1
Assets:
Short-term investment at fair value	667,934	10,268
Derivative assets:
Derivative asset, before netting	55,906	77,219
Total derivative assets	55,906	77,219
Total assets	724,910	88,608
Derivative liabilities:
Derivative liability, before netting	13,672	3,209
Net amounts of liabilities presented in the consolidated balance sheet	13,672	3,209
Total liabilities	13,672	3,209
Recurring basis | Level 1 | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,070	1,121
Recurring basis | Level 1 | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	35,109	66,176
Recurring basis | Level 1 | Call options on Eurodollar futures | Sales
Derivative liabilities:
Derivative liability, before netting	13,672	3,209
Recurring basis | Level 1 | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	20,797	11,043
Recurring basis | Level 2
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	960,267
Loans held for sale	6,131,830	3,942,127
Derivative assets:
Derivative asset, before netting	69,950	91,277
Total derivative assets	69,950	91,277
Total assets	7,162,047	4,033,404
Derivative liabilities:
Derivative liability, before netting	87,342	97,937
Net amounts of liabilities presented in the consolidated balance sheet	87,342	97,937
Total liabilities	87,342	97,937
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	10,878	78,448
Derivative liabilities:
Derivative liability, before netting	50,487	5,141
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	57,180	6,151
Derivative liabilities:
Derivative liability, before netting	36,855	92,796
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting	1,892	413
Recurring basis | Level 2 | MBS call options
Derivative assets:
Derivative asset, before netting		6,265
Recurring basis | Level 3
Assets:
Loans held for sale	433,874	478,564
Derivative assets:
Derivative asset, before netting	120,837	90,313
Total derivative assets	120,837	90,313
Mortgage servicing rights	7,752,292	7,099,348
Total assets	8,307,003	7,668,225
Derivative liabilities:
Derivative liability, before netting	2,222	720
Net amounts of liabilities presented in the consolidated balance sheet	2,222	720
Mortgage servicing liabilities	1,718	1,805
Total liabilities	3,940	2,525
Recurring basis | Level 3 | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	120,837	90,313
Derivative liabilities:
Derivative liability, before netting	$ 2,222	$ 720