Net Interest Income (Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income:
Cash and short-term investments	$ 9,776	$ 2,038	$ 2,356
Loans held for sale at fair value	138,124	128,732	91,972
Placement fees relating to custodial funds	134,498	78,184	40,813
Interest income, excluding related parties	282,398	208,954	135,141
Interest income	288,700	216,416	143,179
Interest expense:
Mortgage loan participation purchase and sale agreements	8,874	8,754	5,496
Obligations under capital lease	693	536	769
Notes payable	69,710	73,610	39,369
Interest shortfall on repayments of mortgage loans serviced for Agency securitizations	41,439	18,777	16,933
Interest on mortgage loan impound deposits	6,757	5,319	4,716
Interest expense, non-affiliates	201,688	129,459	127,569
Interest expense	211,979	144,597	144,520
Net interest income (expense)	76,721	71,819	(1,341)
PMT
Interest income:
From PennyMac Mortgage Investment Trust	6,302	7,462	8,038
Interest expense:
To PennyMac Mortgage Investment Trust	10,291	15,138	16,951
Assets sold under agreements to repurchase
Interest expense:
Assets sold under agreements to repurchase	74,215	22,463	60,286
Incentives recorded	$ 14,700	$ 48,100	$ 9,200