Regulatory Capital and Liquidity Requirements (Details) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2015	Sep. 30, 2018
Fannie Mae / Freddie Mac - PLS
Regulatory Net Worth and Agency Capital Requirements
Net worth	$ 1,561,977,000		$ 1,749,912,000
Capital Requirement	429,671,000		495,694,000
Liquidity	196,415,000		243,827,000
Liquidity requirement	$ 58,754,000		$ 68,224,000
Tangible net worth / Total assets ratio actual	21.00%		22.00%
Tangible net worth / Total assets ratio requirement	6.00%		6.00%
Ginnie Mae - PLS
Regulatory Net Worth and Agency Capital Requirements
Net worth	$ 1,307,580,000		$ 1,520,550,000
Capital Requirement	674,133,000		698,354,000
Liquidity	196,415,000		243,827,000
Liquidity requirement	153,431,000		181,852,000
Ginnie Mae - PennyMac
Regulatory Net Worth and Agency Capital Requirements
Net worth	1,511,201,000		1,755,669,000
Capital Requirement	741,574,000		768,190,000
Ginnie Mae - PennyMac \| 1-4 unit servicing portfolio
Regulatory Net Worth and Agency Capital Requirements
Net worth	$ 2,500,000
FHFA net worth requirement spread	0.35%
FHFA liquidity spread of UPB serviced	0.10%
Liquidity requirement	$ 1,000,000
HUD - PLS
Regulatory Net Worth and Agency Capital Requirements
Net worth	1,307,580,000		1,520,550,000
Capital Requirement	$ 2,500,000		$ 2,500,000
Federal Housing Finance Agency
Regulatory Net Worth and Agency Capital Requirements
Net worth		$ 2,500,000
FHFA liquidity spread of UPB serviced		0.035%
FHFA additional liquidity spread of UPB in excess of 6%		$ 2
Federal Housing Finance Agency \| 1-4 unit servicing portfolio
Regulatory Net Worth and Agency Capital Requirements
FHFA net worth requirement spread		0.25%

The liquidity requirement additional spread of the total non-performing unpaid principal balance in excess of 6.0%.

No definition available.

Name:	pfsi_FederalHousingFinanceAgencyLiquidityRequirementAdditionalSpreadOfTotalNonPerformingUnpaidPrincipalBalanceInExcessOfSixPercent
Namespace Prefix:	pfsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The liquidity requirement spread of the aggregate unpaid principal balance serviced, required by the Federal Housing Finance Agency.

+ References

No definition available.

+ Details

Name:	pfsi_FederalHousingFinanceAgencyLiquidityRequirementSpreadOfAggregateUnpaidPrincipalBalanceServiced
Namespace Prefix:	pfsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The eligibility requirement spread added to the net worth requirement, as a percent of the Company's total servicing portfolio, required by the Federal Housing Finance Agency.

+ References

No definition available.

+ Details

Name:	pfsi_FederalHousingFinanceAgencyNetWorthRequirementSpreadAsPercentOfCompanySServicingPortfolio
Namespace Prefix:	pfsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of total liquidity as defined in the regulations.

+ References

No definition available.

+ Details

Name:	pfsi_Liquidity
Namespace Prefix:	pfsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The lowest amount of liquidity required by secondary market investors or state-imposed regulatory mandates.

+ References

No definition available.

+ Details

Name:	pfsi_MinimumLiquidityRequiredForCompliance
Namespace Prefix:	pfsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The tangible net worth to total assets ratio actual.

+ References

No definition available.

+ Details

Name:	pfsi_TangibleNetWorthTotalAssetsRatioActual
Namespace Prefix:	pfsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The tangible net worth to total assets ratio requirement.

+ References

No definition available.

+ Details

Name:	pfsi_TangibleNetWorthTotalAssetsRatioRequirement
Namespace Prefix:	pfsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

+ Details

Name:	us-gaap_Capital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ComplianceWithRegulatoryCapitalRequirementsForMortgageCompaniesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The lowest amount of net worth (total assets minus total liabilities) required by secondary market investors or state-imposed regulatory mandates.

+ References

+ Details

Name:	us-gaap_MinimumNetWorthRequiredForCompliance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RegulatoryCapitalRequirementsForMortgageCompaniesBySecondaryMarketInvestorAxis=pfsi_FannieMaeFreddieMacMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryCapitalRequirementsForMortgageCompaniesBySecondaryMarketInvestorAxis=pfsi_GovernmentNationalMortgageAssociationIssuerPLSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryCapitalRequirementsForMortgageCompaniesBySecondaryMarketInvestorAxis=pfsi_GovernmentNationalMortgageAssociationIssuersParentPNMACMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=pfsi_OneToFourUnitServicingPortfolioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryCapitalRequirementsForMortgageCompaniesBySecondaryMarketInvestorAxis=pfsi_USDepartmentOfHousingAndUrbanDevelopmentPLSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryCapitalRequirementsForMortgageCompaniesBySecondaryMarketInvestorAxis=pfsi_FederalHousingFinanceAgencyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: