Segments (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segments and Related Information
Number of segments | item									3
Revenues:
Net mortgage loan servicing fees	$ 105,212,000	$ 109,703,000	$ 113,689,000	$ 116,789,000	$ 106,902,000	$ 78,081,000	$ 46,913,000	$ 74,163,000	$ 445,393,000	$ 306,059,000	$ 185,466,000
Net gains on mortgage loans held for sale at fair value	59,748,000	56,914,000	60,946,000	71,414,000	98,621,000	108,136,000	98,091,000	86,956,000	249,022,000	391,804,000	531,780,000
Mortgage loan origination fees	26,165,000	26,485,000	24,428,000	24,563,000	30,267,000	33,168,000	30,193,000	25,574,000	101,641,000	119,202,000	125,534,000
Fulfillment fees from PennyMac Mortgage Investment Trust											86,465,000
Net interest income (expense):
Interest income									216,416,000	143,179,000	81,127,000
Interest expense, before non-segment activities										144,520,000	106,256,000
Net interest expense, before non-segment activities										(1,341,000)
Management fees									24,469,000	23,585,000	22,746,000
Carried Interest from Investment Funds									(365,000)	(1,040,000)	980,000
Other									10,174,000	3,895,000	3,445,000
Total net revenues, before non-segment activities									983,503,000	922,523,000	931,287,000
Expenses	192,895,000	189,232,000	169,600,000	165,205,000	176,861,000	156,491,000	143,761,000	142,441,000	716,932,000	619,554,000	548,804,000
Income (loss) before provision for income taxes and non-segment activities									266,571,000	302,969,000	382,483,000
Non-segment activities									1,126,000	32,940,000	600,000
Income before provision for income taxes	58,306,000	61,697,000	74,698,000	72,996,000	121,773,000	94,144,000	57,960,000	62,032,000	267,697,000	335,909,000	383,083,000
Assets:
Segment assets at year end	7,478,573,000	6,992,530,000	6,841,706,000	6,902,891,000	7,368,093,000	6,388,369,000	6,404,738,000	5,251,377,000	7,478,573,000	7,368,093,000
PMT
Revenues:
Net mortgage loan servicing fees											185,466,000
Fulfillment fees from PennyMac Mortgage Investment Trust	28,591,000	$ 26,256,000	$ 14,559,000	$ 11,944,000	19,175,000	$ 23,507,000	$ 21,107,000	$ 16,570,000	81,350,000	80,359,000	86,465,000
Net interest income (expense):
Management fees									24,465,000	22,584,000	20,657,000
Assets:
Receivable	33,464,000				27,119,000				33,464,000	27,119,000
Investment Funds
Net interest income (expense):
Net interest expense, before non-segment activities											(25,129,000)
Management fees									4,000	1,001,000	2,089,000
Carried Interest from Investment Funds									$ (365,000)	(1,040,000)	980,000
Assets:
Receivable					417,000					417,000
Mortgage banking
Segments and Related Information
Number of segments | item									2
Revenues:
Net mortgage loan servicing fees									$ 445,393,000
Net gains on mortgage loans held for sale at fair value									249,022,000
Mortgage loan origination fees									101,641,000
Net interest income (expense):
Interest income									216,400,000
Interest expense, before non-segment activities									144,548,000
Net interest expense, before non-segment activities									71,852,000
Other									4,658,000
Total net revenues, before non-segment activities									953,916,000
Expenses									694,348,000
Income (loss) before provision for income taxes and non-segment activities									259,568,000
Income before provision for income taxes									259,568,000
Mortgage banking | PMT
Revenues:
Fulfillment fees from PennyMac Mortgage Investment Trust									81,350,000
Operating segment
Net interest income (expense):
Interest expense, before non-segment activities									144,597,000
Net interest expense, before non-segment activities									71,819,000
Assets:
Segment assets at year end	7,478,498,000				7,365,488,000				7,478,498,000	7,365,488,000	5,128,398,000
Non-segment activities change in federal tax rate under the Tax Act										32,000,000
Working capital	75,000				2,600,000				75,000	2,600,000	5,500,000
Operating segment | Investment management
Net interest income (expense):
Interest income									16,000		1,000
Interest expense, before non-segment activities									49,000	49,000	50,000
Net interest expense, before non-segment activities									(33,000)	(49,000)
Management fees									24,469,000	23,585,000	22,746,000
Carried Interest from Investment Funds											980,000
Other									5,516,000	183,000	319,000
Total net revenues, before non-segment activities									29,587,000	22,679,000	23,996,000
Expenses									22,584,000	16,890,000	21,510,000
Income (loss) before provision for income taxes and non-segment activities									7,003,000	5,789,000	2,486,000
Income before provision for income taxes									7,003,000	5,789,000	2,486,000
Assets:
Segment assets at year end	11,681,000				19,880,000				11,681,000	19,880,000	91,517,000
Operating segment | Investment management | Investment Funds
Net interest income (expense):
Net interest expense, before non-segment activities											(49,000)
Carried Interest from Investment Funds									(365,000)	(1,040,000)
Operating segment | Mortgage banking
Revenues:
Net mortgage loan servicing fees										306,059,000
Net gains on mortgage loans held for sale at fair value										391,804,000	531,780,000
Mortgage loan origination fees										119,202,000	125,534,000
Fulfillment fees from PennyMac Mortgage Investment Trust											86,465,000
Net interest income (expense):
Interest income										143,179,000	81,126,000
Interest expense, before non-segment activities										144,471,000	106,206,000
Net interest expense, before non-segment activities										(1,292,000)
Other										3,712,000	3,126,000
Total net revenues, before non-segment activities										899,844,000	907,291,000
Expenses										602,664,000	527,294,000
Income (loss) before provision for income taxes and non-segment activities										297,180,000	379,997,000
Income before provision for income taxes										297,180,000	379,997,000
Assets:
Segment assets at year end	7,466,817,000				7,345,608,000				7,466,817,000	7,345,608,000	5,036,881,000
Operating segment | Mortgage banking | PMT
Revenues:
Net mortgage loan servicing fees											185,466,000
Fulfillment fees from PennyMac Mortgage Investment Trust										80,359,000
Operating segment | Mortgage banking | Investment Funds
Net interest income (expense):
Net interest expense, before non-segment activities											(25,080,000)
Operating segment | Mortgage banking Production
Revenues:
Net gains on mortgage loans held for sale at fair value									141,959,000	286,242,000	464,027,000
Mortgage loan origination fees									101,641,000	119,202,000	125,534,000
Fulfillment fees from PennyMac Mortgage Investment Trust											86,465,000
Net interest income (expense):
Interest income									66,408,000	61,195,000	48,944,000
Interest expense, before non-segment activities									7,371,000	35,359,000	32,669,000
Net interest expense, before non-segment activities									59,037,000	25,836,000
Other									2,008,000	2,002,000	2,104,000
Total net revenues, before non-segment activities									385,995,000	513,641,000	694,405,000
Expenses									298,729,000	275,133,000	278,309,000
Income (loss) before provision for income taxes and non-segment activities									87,266,000	238,508,000	416,096,000
Income before provision for income taxes									87,266,000	238,508,000	416,096,000
Assets:
Segment assets at year end	2,434,897,000				2,459,014,000				2,434,897,000	2,459,014,000	2,195,330,000
Operating segment | Mortgage banking Production | PMT
Revenues:
Fulfillment fees from PennyMac Mortgage Investment Trust									81,350,000	80,359,000
Operating segment | Mortgage banking Production | Investment Funds
Net interest income (expense):
Net interest expense, before non-segment activities											16,275,000
Operating segment | Mortgage banking Servicing
Revenues:
Net mortgage loan servicing fees									445,393,000	306,059,000
Net gains on mortgage loans held for sale at fair value									107,063,000	105,562,000	67,753,000
Net interest income (expense):
Interest income									149,992,000	81,984,000	32,182,000
Interest expense, before non-segment activities									137,177,000	109,112,000	73,537,000
Net interest expense, before non-segment activities									12,815,000	(27,128,000)
Other									2,650,000	1,710,000	1,022,000
Total net revenues, before non-segment activities									567,921,000	386,203,000	212,886,000
Expenses									395,619,000	327,531,000	248,985,000
Income (loss) before provision for income taxes and non-segment activities									172,302,000	58,672,000	(36,099,000)
Income before provision for income taxes									172,302,000	58,672,000	(36,099,000)
Assets:
Segment assets at year end	$ 5,031,920,000				$ 4,886,594,000				$ 5,031,920,000	$ 4,886,594,000	2,841,551,000
Operating segment | Mortgage banking Servicing | PMT
Revenues:
Net mortgage loan servicing fees											185,466,000
Operating segment | Mortgage banking Servicing | Investment Funds
Net interest income (expense):
Net interest expense, before non-segment activities											$ (41,355,000)