Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Short-term investments at fair value	$ 24,850	$ 15,217
Loans held for sale	13,385,789	11,616,400
Derivative assets:
Derivative asset, before netting	889,754	847,831
Netting	(358,902)	(136,593)
Total derivative assets	530,852	711,238
Derivative liabilities:
Derivative liability, before netting	302,320	255,360
Netting	(233,763)	(212,722)
Net amounts of liabilities presented in the consolidated balance sheet	68,557	42,638
Mortgage servicing liabilities	46,026	45,324
PMT
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,470	1,105
Interest rate lock commitments
Derivative assets:
Total derivative assets	362,923	679,961
Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	14,318	133,267
Derivative liabilities:
Derivative liability, before netting	192,793	1,276
Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	333,198	1,451
Derivative liabilities:
Derivative liability, before netting	32,729	251,149
MBS put options
Derivative assets:
Derivative asset, before netting	99,670	14,302
Derivative liabilities:
Derivative liability, before netting	34,873
Call options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting	1,539	1,391
Call options on interest rate futures | Sales
Derivative liabilities:
Derivative liability, before netting	1,061
Put options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting	27,133	5,520
Put options on interest rate futures | Sales
Derivative liabilities:
Derivative liability, before netting	15,881
Level 3
Assets:
Loans held for sale	5,202,065	4,675,169
Level 3 | Interest rate lock commitments
Assets:
Loans held for sale	337,940	677,026
Recurring basis
Assets:
Short-term investments at fair value	24,850	15,217
Loans held for sale	13,385,789	11,616,400
Derivative assets:
Derivative asset, before netting	889,754	847,831
Netting	(358,902)	(136,593)
Total derivative assets	530,852	711,238
Mortgage servicing rights at fair value	3,268,910	2,581,174
Total assets	17,211,871	14,925,134
Derivative liabilities:
Derivative liability, before netting	302,320	255,360
Netting	(233,763)	(212,722)
Net amounts of liabilities presented in the consolidated balance sheet	68,557	42,638
Mortgage servicing liabilities	46,026	45,324
Total liabilities	114,583	219,712
Recurring basis | PMT
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,470	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	362,923	679,961
Derivative liabilities:
Derivative liability, before netting	24,983	2,935
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	14,318	133,267
Derivative liabilities:
Derivative liability, before netting	192,793	1,276
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	333,198	1,451
Derivative liabilities:
Derivative liability, before netting	32,729	251,149
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting	99,670	14,302
Derivative liabilities:
Derivative liability, before netting	34,873
Recurring basis | Swaptions | Purchases
Derivative assets:
Derivative asset, before netting	50,973	11,939
Recurring basis | Call options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting	1,539	1,391
Recurring basis | Call options on interest rate futures | Sales
Derivative liabilities:
Derivative liability, before netting	1,061
Recurring basis | Put options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting	27,133	5,520
Recurring basis | Put options on interest rate futures | Sales
Derivative liabilities:
Derivative liability, before netting	15,881
Recurring basis | Level 1
Assets:
Short-term investments at fair value	24,850	15,217
Derivative assets:
Derivative asset, before netting	28,672	6,911
Total derivative assets	28,672	6,911
Total assets	54,992	23,233
Derivative liabilities:
Derivative liability, before netting	16,942
Net amounts of liabilities presented in the consolidated balance sheet	16,942
Total liabilities	16,942
Recurring basis | Level 1 | PMT
Derivative assets:
Investment in PennyMac Mortgage Investment Trust	1,470	1,105
Recurring basis | Level 1 | Call options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting	1,539	1,391
Recurring basis | Level 1 | Call options on interest rate futures | Sales
Derivative liabilities:
Derivative liability, before netting	1,061
Recurring basis | Level 1 | Put options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting	27,133	5,520
Recurring basis | Level 1 | Put options on interest rate futures | Sales
Derivative liabilities:
Derivative liability, before netting	15,881
Recurring basis | Level 2
Assets:
Loans held for sale	8,183,724	6,941,231
Derivative assets:
Derivative asset, before netting	498,159	160,959
Total derivative assets	498,159	160,959
Total assets	8,681,883	7,102,190
Derivative liabilities:
Derivative liability, before netting	260,395	252,425
Net amounts of liabilities presented in the consolidated balance sheet	260,395	252,425
Total liabilities	260,395	252,425
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting	14,318	133,267
Derivative liabilities:
Derivative liability, before netting	192,793	1,276
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting	333,198	1,451
Derivative liabilities:
Derivative liability, before netting	32,729	251,149
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting	99,670	14,302
Derivative liabilities:
Derivative liability, before netting	34,873
Recurring basis | Level 2 | Swaptions | Purchases
Derivative assets:
Derivative asset, before netting	50,973	11,939
Recurring basis | Level 3
Assets:
Loans held for sale	5,202,065	4,675,169
Derivative assets:
Derivative asset, before netting	362,923	679,961
Total derivative assets	362,923	679,961
Mortgage servicing rights at fair value	3,268,910	2,581,174
Total assets	8,833,898	7,936,304
Derivative liabilities:
Derivative liability, before netting	24,983	2,935
Net amounts of liabilities presented in the consolidated balance sheet	24,983	2,935
Mortgage servicing liabilities	46,026	45,324
Total liabilities	71,009	180,009
Recurring basis | Level 3 | PMT
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	362,923	679,961
Derivative liabilities:
Derivative liability, before netting	$ 24,983	$ 2,935