Derivative Instruments - Summary of Change in Fair Value Reclassified or Expected to be Reclassified from Accumulated Other Comprehensive Loss to Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Amount released to pre - tax earnings	$ 5,683	$ 5,451	$ 17,357	$ 17,019
Amount released to pre - tax earnings	98,408	87,346	301,741	264,179
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] \| Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
Derivative [Line Items]
Amount released to pre - tax earnings	7	11	16	24
Amount released to pre - tax earnings	(53)	139	239	448
Foreign Currency Purchase Contracts [Member] \| Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] \| Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
Derivative [Line Items]
Estimated to be Reclassified in the Next 12 Months	27		27
Amount released to pre - tax earnings	7	11	16	24
Futures Contracts - Copper and Aluminum [Member] \| Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] \| Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
Derivative [Line Items]
Estimated to be Reclassified in the Next 12 Months	(258)		(258)
Amount released to pre - tax earnings	$ (53)	$ 139	$ 239	$ 448

The aggregate cost of goods produced and sold during the reporting period, excluding depreciation, depletion, and amortization.

No definition available.

+ Details

Name:	us-gaap_CostOfGoodsSoldExcludingDepreciationDepletionAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

Name:	us-gaap_DepreciationAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Definition

The estimated net amount of unrealized gains or losses on foreign currency cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994

+ Details

Name:	us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis=us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ap_ForeignCurrencyPurchasesContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ap_FuturesContractsCopperAndAluminumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: