Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024
Assets:
Short-term investment at fair value	$ 462,262		$ 420,553
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	784,958		825,865
Loans held for sale	6,961,224		8,217,468
Derivative assets:
Derivative asset, before netting	270,518		232,293
Netting	(89,876)		(119,217)
Total derivative assets	180,642		113,076
Investment in PennyMac Mortgage Investment Trust	965		944
Derivative liabilities:
Derivative liability, before netting	170,411		102,881
Netting	(137,908)		(61,981)
Net amounts of liabilities presented in the consolidated balance sheet	32,503		40,900
Derivative liability to PMT	1,038
Mortgage servicing liabilities	1,643		1,683
Principal-Only-Strip MBS
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	784,958	$ 817,596	825,865	$ 914,223	$ 524,576
Recurring basis
Assets:
Short-term investment at fair value	462,262		420,553
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	784,958		825,865
Loans held for sale	6,961,224		8,217,468
Derivative assets:
Derivative asset, before netting	270,518		232,293
Netting	(89,876)		(119,217)
Total derivative assets	180,642		113,076
Mortgage servicing rights	9,531,249		8,744,528
Total assets	17,921,300		18,322,434
Derivative liabilities:
Derivative liability, before netting	170,411		102,881
Netting	(137,908)		(61,981)
Net amounts of liabilities presented in the consolidated balance sheet	32,503		40,900
Derivative liability to PMT	1,038
Mortgage servicing liabilities	1,643		1,683
Total liabilities	35,184		42,583
Recurring basis | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	965		944
Recurring basis | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	143,061		56,946
Derivative liabilities:
Derivative liability, before netting	908		23,381
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	89,834		3,701
Derivative liabilities:
Derivative liability, before netting	174		66,646
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	2,939		152,526
Derivative liabilities:
Derivative liability, before netting	159,266		12,854
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting			3,278
Recurring basis | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	33,688		3,250
Recurring basis | Call options on Eurodollar futures | Sales
Derivative liabilities:
Derivative liability, before netting	10,063
Recurring basis | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	996		12,592
Recurring basis | Level 1
Assets:
Short-term investment at fair value	462,262		420,553
Derivative assets:
Derivative asset, before netting	34,684		15,842
Total derivative assets	34,684		15,842
Total assets	497,911		437,339
Derivative liabilities:
Derivative liability, before netting	10,063
Net amounts of liabilities presented in the consolidated balance sheet	10,063
Total liabilities	10,063
Recurring basis | Level 1 | Related Party | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	965		944
Recurring basis | Level 1 | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	33,688		3,250
Recurring basis | Level 1 | Call options on Eurodollar futures | Sales
Derivative liabilities:
Derivative liability, before netting	10,063
Recurring basis | Level 1 | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	996		12,592
Recurring basis | Level 2
Assets:
Principal-only stripped mortgage-backed securities at fair value pledged to creditors	784,958		825,865
Loans held for sale	6,450,311		7,783,415
Derivative assets:
Derivative asset, before netting	92,773		159,505
Total derivative assets	92,773		159,505
Total assets	7,328,042		8,768,785
Derivative liabilities:
Derivative liability, before netting	159,440		79,500
Net amounts of liabilities presented in the consolidated balance sheet	159,440		79,500
Derivative liability to PMT	1,038
Total liabilities	160,478		79,500
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	89,834		3,701
Derivative liabilities:
Derivative liability, before netting	174		66,646
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	2,939		152,526
Derivative liabilities:
Derivative liability, before netting	159,266		12,854
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting			3,278
Recurring basis | Level 3
Assets:
Loans held for sale	510,913		434,053
Derivative assets:
Derivative asset, before netting	143,061		56,946
Total derivative assets	143,061		56,946
Mortgage servicing rights	9,531,249		8,744,528
Total assets	10,185,223		9,235,527
Derivative liabilities:
Derivative liability, before netting	908		23,381
Net amounts of liabilities presented in the consolidated balance sheet	908		23,381
Mortgage servicing liabilities	1,643		1,683
Total liabilities	2,551		25,064
Recurring basis | Level 3 | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	143,061		56,946
Derivative liabilities:
Derivative liability, before netting	$ 908		$ 23,381