Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the impact on the weighted average interest rate from interest rate swaps for the period.

+ References

No definition available.

+ Details

Name:	pag_InterestRateImpactFromSwaps
Namespace Prefix:	pag_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226003-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

+ Details

Name:	us-gaap_DerivativeLiabilityFairValueGrossAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeByNatureAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeByNatureAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=pag_FloatingRateFloorPlanDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=pag_DebtInstrumentFixedRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivatives and Hedging (Details) - USD ($) $ in Millions	9 Months Ended
Derivatives and Hedging (Details) - USD ($) $ in Millions	Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014
Forward foreign exchange contracts \| Level 2
Derivative
Estimated asset of contracts designated as hedging instruments, fair value		$ 1.6	$ 1.1
Interest Rate Swap Agreements \| Floating Rate Floor Plan Debt
Derivative
Increase in the weighted average interest rate on floor plan borrowings due to the swaps (as a percent)	0.29%
Interest Rate Swap Agreements \| Floating Rate Floor Plan Debt \| LIBOR portion
Derivative
Portion of floating rate floor plan debt fixed by swap agreements			$ 300.0
Interest rate swap, fixed (as a percent)			2.135%
Interest Rate Swap Agreements \| Floating Rate Floor Plan Debt \| Fixed rate portion
Derivative
Portion of floating rate floor plan debt fixed by swap agreements			$ 100.0
Interest rate swap, fixed (as a percent)			1.55%