Net Interest Income (Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income:
Short-term investments	$ 2,038	$ 2,356	$ 2,558
Mortgage loans held for sale at fair value	128,732	91,972	54,584
Placement fees relating to custodial funds	78,184	40,813	16,155
Interest income, excluding related parties	208,954	135,141	73,297
Interest income	216,416	143,179	81,127
Interest expense:
Mortgage loan participation purchase and sale agreements	8,754	5,496	5,523
Notes payable	73,610	39,369	8,688
Obligations under capital lease	536	769	510
Interest shortfall on repayments of mortgage loans serviced for Agency securitizations	18,777	16,933	15,102
Interest on mortgage loan impound deposits	5,319	4,716	3,991
Interest expense, non-affiliates	129,459	127,569	83,605
Interest expense	144,597	144,520	106,206
Net interest income (expense):	71,819	(1,341)	(25,079)
PMT
Interest income:
From PennyMac Mortgage Investment Trust	7,462	8,038	7,830
Interest expense:
To PennyMac Mortgage Investment Trust Excess servicing spread financing at fair value	15,138	16,951	22,601
Assets sold under agreements to repurchase
Interest expense:
Assets sold under agreements to repurchase	22,463	60,286	$ 49,791
Incentives recorded	$ 48,100	$ 9,200