Net Interest Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest income:
Cash and short-term investments	$ 987	$ 1,711
Loans held for sale at fair value	74,824	46,426
Placement fees relating to custodial funds	5,883	23,209
Interest income, excluding related parties	81,694	71,346
Interest income	82,081	72,564
Interest expense:
Assets sold under agreements to repurchase	52,179	25,684
Mortgage loan participation purchase and sale agreements	1,095	1,810
Obligations under capital lease	59	167
Notes payable	9,888	14,846
Unsecured senior notes	12,670
Corporate revolving line of credit		503
Interest shortfall on repayments of mortgage loans serviced for Agency securitizations	29,436	14,871
Interest on mortgage loan impound deposits	1,106	1,657
Interest expense, non-affiliates	106,433	59,538
Interest expense	107,713	61,512
Net interest (expense) income	(25,632)	11,052
PMT
Interest income:
From PennyMac Mortgage Investment Trust	387	1,218
Interest expense:
To PennyMac Mortgage Investment Trust Excess servicing spread financing at fair value	1,280	1,974
Assets sold under agreements to repurchase
Interest expense:
Assets sold under agreements to repurchase	$ 52,179	$ 25,684