Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Assets:
Short-term investment at fair value	$ 420,553	$ 10,268
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	825,865
Loans held for sale	8,217,468	4,420,691
Derivative assets:
Derivative asset, before netting	232,293	258,809
Netting	(119,217)	(79,730)
Total derivative assets	113,076	179,079
Investment in PennyMac Mortgage Investment Trust	944	1,121
Derivative liabilities:
Derivative liability, before netting	102,881	101,866
Netting	(61,981)	(48,591)
Net amounts of liabilities presented in the consolidated balance sheet	40,900	53,275
Mortgage servicing liabilities	1,683	1,805
Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	944	1,121
Principal-Only-Strip MBS
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	825,865
Recurring basis
Assets:
Short-term investment at fair value	420,553	10,268
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	825,865
Loans held for sale	8,217,468	4,420,691
Derivative assets:
Derivative asset, before netting	232,293	258,809
Netting	(119,217)	(79,730)
Total derivative assets	113,076	179,079
Mortgage servicing rights	8,744,528	7,099,348
Total assets	18,322,434	11,710,507
Derivative liabilities:
Derivative liability, before netting	102,881	101,866
Netting	(61,981)	(48,591)
Net amounts of liabilities presented in the consolidated balance sheet	40,900	53,275
Mortgage servicing liabilities	1,683	1,805
Total liabilities	42,583	55,080
Recurring basis | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	944	1,121
Recurring basis | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	56,946	90,313
Derivative liabilities:
Derivative liability, before netting	23,381	720
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	3,701	78,448
Derivative liabilities:
Derivative liability, before netting	66,646	5,141
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	152,526	6,151
Derivative liabilities:
Derivative liability, before netting	12,854	92,796
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting	3,278	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	3,250	66,176
Recurring basis | Call options on Eurodollar futures | Sales
Derivative liabilities:
Derivative liability, before netting		3,209
Recurring basis | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	12,592	11,043
Recurring basis | Level 1
Assets:
Short-term investment at fair value	420,553	10,268
Derivative assets:
Derivative asset, before netting	15,842	77,219
Total derivative assets	15,842	77,219
Total assets	437,339	88,608
Derivative liabilities:
Derivative liability, before netting		3,209
Net amounts of liabilities presented in the consolidated balance sheet		3,209
Total liabilities		3,209
Recurring basis | Level 1 | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	944	1,121
Recurring basis | Level 1 | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	3,250	66,176
Recurring basis | Level 1 | Call options on Eurodollar futures | Sales
Derivative liabilities:
Derivative liability, before netting		3,209
Recurring basis | Level 1 | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	12,592	11,043
Recurring basis | Level 2
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	825,865
Loans held for sale	7,783,415	3,942,127
Derivative assets:
Derivative asset, before netting	159,505	91,277
Total derivative assets	159,505	91,277
Total assets	8,768,785	4,033,404
Derivative liabilities:
Derivative liability, before netting	79,500	97,937
Net amounts of liabilities presented in the consolidated balance sheet	79,500	97,937
Total liabilities	79,500	97,937
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	3,701	78,448
Derivative liabilities:
Derivative liability, before netting	66,646	5,141
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	152,526	6,151
Derivative liabilities:
Derivative liability, before netting	12,854	92,796
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting	3,278	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	434,053	478,564
Derivative assets:
Derivative asset, before netting	56,946	90,313
Total derivative assets	56,946	90,313
Mortgage servicing rights	8,744,528	7,099,348
Total assets	9,235,527	7,668,225
Derivative liabilities:
Derivative liability, before netting	23,381	720
Net amounts of liabilities presented in the consolidated balance sheet	23,381	720
Mortgage servicing liabilities	1,683	1,805
Total liabilities	25,064	2,525
Recurring basis | Level 3 | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	56,946	90,313
Derivative liabilities:
Derivative liability, before netting	$ 23,381	$ 720