Net Interest (Expense) Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Interest income:
Cash and short-term investments	$ 747	$ 1,893	$ 1,734	$ 3,604
Loans held for sale at fair value	76,453	32,586	151,277	79,012
Placement fees relating to custodial funds	3,597	12,047	9,480	35,256
Interest income, excluding related parties	80,797	46,526	162,491	117,872
Interest income	80,797	47,318	162,878	119,882
Interest expense:
Assets sold under agreements to repurchase	44,623	17,487	96,802	43,171
Mortgage loan participation purchase and sale agreements	1,039	1,061	2,134	2,871
Obligations under capital lease	48	104	107	271
Notes payable	10,104	11,109	19,992	25,955
Unsecured senior notes	16,169		28,839
Corporate revolving line of credit		472		975
Interest shortfall on repayments of mortgage loans serviced for Agency securitizations	29,144	18,954	58,580	33,825
Interest on mortgage loan impound deposits	1,304	1,648	2,410	3,305
Interest expense, non-affiliates	102,431	50,835	208,864	110,373
Interest expense	102,431	53,207	210,144	114,719
Net interest (expense) income	(21,634)	(5,889)	(47,266)	5,163
PMT
Interest income:
From PennyMac Mortgage Investment Trust		792	387	2,010
Interest expense:
To PennyMac Mortgage Investment Trust Excess servicing spread financing at fair value		2,372	1,280	4,346
Assets sold under agreements to repurchase
Interest expense:
Assets sold under agreements to repurchase	$ 44,623	$ 17,487	$ 96,802	$ 43,171