Segments and Related Information - Financial Highlights by Segment (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segments and Related Information
Number of segments | segment			3
Revenues:
Net mortgage loan servicing fees	$ 109,703	$ 78,081	$ 340,181	$ 199,157
Net gains on mortgage loans held for sale at fair value	56,914	108,136	189,274	293,183
Mortgage loan origination fees	26,485	33,168	75,476	88,935
Net interest income (expense):
Interest income	60,964	44,442	158,683	103,274
Interest expense, before non-segment activities	38,775	42,492	108,136	108,843
Net interest expense, before non-segment activities	22,189	1,950	50,547	(5,569)
Management fees	6,471	6,216	17,910	17,597
Other	2,928	735	7,646	3,387
Total net revenues, before non-segment activities	250,929	250,635	733,428	656,829
Expenses	189,232	156,491	524,037	442,693
Income before provision for income taxes	61,697	94,144	209,391	214,136
Assets:
Segment assets at quarter end	6,992,530		6,992,530		$ 7,368,093
PMT
Revenues:
Fulfillment fees from PennyMac Mortgage Investment Trust	26,256	23,507	52,759	61,184
Net interest income (expense):
Management fees	6,482	6,038	17,906	16,684
Assets:
Receivable	27,467		27,467		27,119
Investment Funds
Net interest income (expense):
Management fees	(11)	178	4	913
Carried Interest from Investment Funds	(17)	(1,158)	$ (365)	(1,045)
Assets:
Receivable					$ 417
Mortgage banking
Segments and Related Information
Number of segments | segment			2
Operating segment
Assets:
Segment assets at quarter end	6,993,020	6,386,724	$ 6,993,020	6,386,724
Working capital	1,800	1,600	1,800	1,600
Receivable	2,300		2,300
Operating segment | Investment management
Net interest income (expense):
Interest income	16		16
Interest expense, before non-segment activities	10	13	41	37
Net interest expense, before non-segment activities	6	(13)	(25)	(37)
Management fees	6,471	6,216	17,910	17,597
Other	1,478	(25)	4,221	234
Total net revenues, before non-segment activities	7,938	5,020	21,741	16,749
Expenses	5,481	4,305	17,221	12,455
Income before provision for income taxes	2,457	715	4,520	4,294
Assets:
Segment assets at quarter end	11,996	20,369	11,996	20,369
Operating segment | Investment management | Investment Funds
Net interest income (expense):
Carried Interest from Investment Funds	(17)	(1,158)	(365)	(1,045)
Operating segment | Mortgage banking
Revenues:
Net mortgage loan servicing fees	109,703	78,081	340,181	199,157
Net gains on mortgage loans held for sale at fair value	56,914	108,136	189,274	293,183
Mortgage loan origination fees	26,485	33,168	75,476	88,935
Net interest income (expense):
Interest income	60,948	44,442	158,667	103,274
Interest expense, before non-segment activities	38,765	42,479	108,095	108,806
Net interest expense, before non-segment activities	22,183	1,963	50,572	(5,532)
Other	1,450	760	3,425	3,153
Total net revenues, before non-segment activities	242,991	245,615	711,687	640,080
Expenses	183,751	152,186	506,816	430,238
Income before provision for income taxes	59,240	93,429	204,871	209,842
Assets:
Segment assets at quarter end	6,981,024	6,366,355	6,981,024	6,366,355
Operating segment | Mortgage banking | PMT
Revenues:
Fulfillment fees from PennyMac Mortgage Investment Trust	26,256	23,507	52,759	61,184
Operating segment | Mortgage banking Production
Revenues:
Net gains on mortgage loans held for sale at fair value	34,947	79,983	105,111	217,526
Mortgage loan origination fees	26,485	33,168	75,476	88,935
Net interest income (expense):
Interest income	17,013	17,651	48,135	45,866
Interest expense, before non-segment activities	1,274	12,355	4,401	32,507
Net interest expense, before non-segment activities	15,739	5,296	43,734	13,359
Other	645	235	1,497	1,711
Total net revenues, before non-segment activities	104,072	142,189	278,577	382,715
Expenses	78,405	73,231	216,722	199,547
Income before provision for income taxes	25,667	68,958	61,855	183,168
Assets:
Segment assets at quarter end	2,168,126	2,737,666	2,168,126	2,737,666
Operating segment | Mortgage banking Production | PMT
Revenues:
Fulfillment fees from PennyMac Mortgage Investment Trust	26,256	23,507	52,759	61,184
Operating segment | Mortgage banking Servicing
Revenues:
Net mortgage loan servicing fees	109,703	78,081	340,181	199,157
Net gains on mortgage loans held for sale at fair value	21,967	28,153	84,163	75,657
Net interest income (expense):
Interest income	43,935	26,791	110,532	57,408
Interest expense, before non-segment activities	37,491	30,124	103,694	76,299
Net interest expense, before non-segment activities	6,444	(3,333)	6,838	(18,891)
Other	805	525	1,928	1,442
Total net revenues, before non-segment activities	138,919	103,426	433,110	257,365
Expenses	105,346	78,955	290,094	230,691
Income before provision for income taxes	33,573	24,471	143,016	26,674
Assets:
Segment assets at quarter end	$ 4,812,898	$ 3,628,689	$ 4,812,898	$ 3,628,689