Fair Value - Financial Statement Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Fair value
Interest rate threshold used in determination of accounting for loans underlying mortgage servicing rights (as a percent)	4.50%
Assets:
Short-term investments at fair value		$ 74,611				$ 117,824
Loans held for sale		4,912,953	$ 4,522,971	$ 3,506,406	$ 2,668,929	2,521,647	$ 2,416,955	$ 2,527,231	$ 2,584,236
Derivative assets:
Derivative asset, before netting		187,397				123,316
Netting		(27,711)				(26,969)
Total derivative assets		159,686				96,347
Mortgage servicing rights at fair value		2,920,603				2,807,333
Derivative liabilities:
Derivative liability, before netting		38,946				28,146
Netting		(16,616)				(25,082)
Net amounts of liabilities presented in the consolidated balance sheet		22,330				3,064
Mortgage servicing liabilities		29,140				8,681
PMT
Derivative assets:
Investment in PennyMac Mortgage Investment Trust		1,672				1,397
Interest rate lock commitments
Derivative assets:
Total derivative assets		138,511				50,507
Level 3 | Interest rate lock commitments
Assets:
Loans held for sale		136,650				49,338
Recurring basis
Assets:
Short-term investments at fair value		74,611				117,824
Loans held for sale		4,912,953				2,521,647
Derivative assets:
Derivative asset, before netting		187,397				123,316
Netting		(27,711)				(26,969)
Total derivative assets		159,686				96,347
Mortgage servicing rights at fair value		2,926,790				2,820,612
Total assets		8,075,712				5,557,827
Derivative liabilities:
Derivative liability, before netting		38,946				28,146
Netting		(16,616)				(25,082)
Net amounts of liabilities presented in the consolidated balance sheet		22,330				3,064
Mortgage servicing liabilities		29,140				8,681
Total liabilities		230,056				227,855
Recurring basis | PMT
Derivative assets:
Investment in PennyMac Mortgage Investment Trust		1,672				1,397
Derivative liabilities:
Excess servicing spread financing at fair value to affiliate		178,586				216,110
Recurring basis | Repurchase agreement derivatives
Derivative assets:
Derivative asset, before netting						26,770
Recurring basis | MBS call options
Derivative assets:
Derivative asset, before netting						2,135
Recurring basis | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting		138,511				50,507
Derivative liabilities:
Derivative liability, before netting		1,861				1,169
Recurring basis | Repurchase agreement derivatives
Derivative assets:
Derivative asset, before netting		8,187
Recurring basis | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting		12,364				35,916
Derivative liabilities:
Derivative liability, before netting		19,040				215
Recurring basis | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting		17,097				437
Derivative liabilities:
Derivative liability, before netting		18,045				26,762
Recurring basis | MBS put options
Derivative assets:
Derivative asset, before netting		3,415				720
Recurring basis | Swaptions
Derivative assets:
Derivative asset, before netting		2,409
Recurring basis | Call options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting		1,469				5,965
Recurring basis | Put options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting		3,945				866
Recurring basis | Level 1
Assets:
Short-term investments at fair value		74,611				117,824
Derivative assets:
Derivative asset, before netting		5,414				6,831
Total derivative assets		5,414				6,831
Total assets		81,697				126,052
Recurring basis | Level 1 | PMT
Derivative assets:
Investment in PennyMac Mortgage Investment Trust		1,672				1,397
Recurring basis | Level 1 | Call options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting		1,469				5,965
Recurring basis | Level 1 | Put options on interest rate futures | Purchases
Derivative assets:
Derivative asset, before netting		3,945				866
Recurring basis | Level 2
Assets:
Loans held for sale		4,529,075				2,261,639
Derivative assets:
Derivative asset, before netting		35,285				39,208
Total derivative assets		35,285				39,208
Total assets		4,564,360				2,300,847
Derivative liabilities:
Derivative liability, before netting		37,085				26,977
Net amounts of liabilities presented in the consolidated balance sheet		37,085				26,977
Total liabilities		37,085				26,977
Recurring basis | Level 2 | MBS call options
Derivative assets:
Derivative asset, before netting						2,135
Recurring basis | Level 2 | Forward contracts | Purchases
Derivative assets:
Derivative asset, before netting		12,364				35,916
Derivative liabilities:
Derivative liability, before netting		19,040				215
Recurring basis | Level 2 | Forward contracts | Sales
Derivative assets:
Derivative asset, before netting		17,097				437
Derivative liabilities:
Derivative liability, before netting		18,045				26,762
Recurring basis | Level 2 | MBS put options
Derivative assets:
Derivative asset, before netting		3,415				720
Recurring basis | Level 2 | Swaptions
Derivative assets:
Derivative asset, before netting		2,409
Recurring basis | Level 3
Assets:
Loans held for sale		383,878				260,008
Derivative assets:
Derivative asset, before netting		146,698				77,277
Total derivative assets		146,698				77,277
Mortgage servicing rights at fair value		2,926,790				2,820,612
Total assets		3,457,366				3,157,897
Derivative liabilities:
Derivative liability, before netting		1,861				1,169
Net amounts of liabilities presented in the consolidated balance sheet		1,861				1,169
Mortgage servicing liabilities		29,140				8,681
Total liabilities		209,587				225,960
Recurring basis | Level 3 | PMT
Derivative liabilities:
Excess servicing spread financing at fair value to affiliate		178,586				216,110
Recurring basis | Level 3 | Repurchase agreement derivatives
Derivative assets:
Derivative asset, before netting						26,770
Recurring basis | Level 3 | Interest rate lock commitments
Derivative assets:
Derivative asset, before netting		138,511				50,507
Derivative liabilities:
Derivative liability, before netting		1,861				$ 1,169
Recurring basis | Level 3 | Repurchase agreement derivatives
Derivative assets:
Derivative asset, before netting		$ 8,187