Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Short-term investment at fair value	$ 6,873	$ 15,217
Loans held for sale	9,742,483	11,616,400
Derivative assets:
Derivative asset, before netting	398,672	847,831
Netting	(64,977)	(136,593)
Total derivative assets	333,695	711,238
Derivative liabilities:
Derivative liability, before netting	54,702	255,360
Netting	(32,096)	(212,722)
Net amounts of liabilities presented in the consolidated balance sheet	22,606	42,638
Mortgage servicing liabilities	2,816	45,324
PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,300	1,105
Interest rate lock commitments
Derivative assets:
Total derivative assets	323,473	679,961
Recurring basis
Assets:
Short-term investment at fair value	6,873	15,217
Loans held for sale	9,742,483	11,616,400
Derivative assets:
Derivative asset, before netting	398,672	847,831
Netting	(64,977)	(136,593)
Total derivative assets	333,695	711,238
Mortgage servicing rights at fair value	3,878,078	2,581,174
Total assets	13,962,429	14,925,134
Derivative liabilities:
Derivative liability, before netting	54,702	255,360
Netting	(32,096)	(212,722)
Net amounts of liabilities presented in the consolidated balance sheet	22,606	42,638
Mortgage servicing liabilities	2,816	45,324
Total liabilities	25,422	219,712
Recurring basis | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,300	1,105
Derivative liabilities:
Excess servicing spread financing at fair value to affiliate		131,750
Recurring basis | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	323,473	679,961
Derivative liabilities:
Derivative liability, before netting	1,280	2,935
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	20,485	133,267
Derivative liabilities:
Derivative liability, before netting	18,007	1,276
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	40,215	1,451
Derivative liabilities:
Derivative liability, before netting	35,415	251,149
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting	7,655	14,302
Recurring basis | Swaptions
Derivative assets:
Derivative asset, before netting	1,625	11,939
Recurring basis | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	2,078	1,391
Recurring basis | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	3,141	5,520
Recurring basis | Level 1
Assets:
Short-term investment at fair value	6,873	15,217
Derivative assets:
Derivative asset, before netting	5,219	6,911
Total derivative assets	5,219	6,911
Total assets	13,392	23,233
Recurring basis | Level 1 | PennyMac Mortgage Investment Trust
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,300	1,105
Recurring basis | Level 1 | Call options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	2,078	1,391
Recurring basis | Level 1 | Put options on Eurodollar futures | Purchases
Derivative assets:
Derivative asset, before netting	3,141	5,520
Recurring basis | Level 2
Assets:
Loans held for sale	8,613,607	6,941,231
Derivative assets:
Derivative asset, before netting	69,980	160,959
Total derivative assets	69,980	160,959
Total assets	8,683,587	7,102,190
Derivative liabilities:
Derivative liability, before netting	53,422	252,425
Net amounts of liabilities presented in the consolidated balance sheet	53,422	252,425
Total liabilities	53,422	252,425
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	20,485	133,267
Derivative liabilities:
Derivative liability, before netting	18,007	1,276
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	40,215	1,451
Derivative liabilities:
Derivative liability, before netting	35,415	251,149
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting	7,655	14,302
Recurring basis | Level 2 | Swaptions
Derivative assets:
Derivative asset, before netting	1,625	11,939
Recurring basis | Level 3
Assets:
Loans held for sale	1,128,876	4,675,169
Derivative assets:
Derivative asset, before netting	323,473	679,961
Total derivative assets	323,473	679,961
Mortgage servicing rights at fair value	3,878,078	2,581,174
Total assets	5,330,427	7,936,304
Derivative liabilities:
Derivative liability, before netting	1,280	2,935
Net amounts of liabilities presented in the consolidated balance sheet	1,280	2,935
Mortgage servicing liabilities	2,816	45,324
Total liabilities	4,096	180,009
Recurring basis | Level 3 | PennyMac Mortgage Investment Trust
Derivative liabilities:
Excess servicing spread financing at fair value to affiliate		131,750
Recurring basis | Level 3 | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting	323,473	679,961
Derivative liabilities:
Derivative liability, before netting	$ 1,280	$ 2,935