Fair Value Measurements - Carrying Amount and Fair Values of the Company's Financial Assets and Liabilities Measured on a Recurring Basis (Detail) - Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount [Member]
Non-derivatives:
Cash and cash equivalents	$ 91.4	$ 90.2
Non-derivatives:
Long-term debt (including current portion)	223.9	218.4
Finance leases (including current portion)	3.8	5.9
Carrying Amount [Member] \| Bank Overdrafts [Member]
Non-derivatives:
Bank overdraft	0.5	0.0
Carrying Amount [Member] \| Derivatives (Level 1 Measurement) [Member] \| Foreign Currency Forward Exchange Contracts [Member]
Derivatives (Level 1 measurement):
Derivative asset	0.0	1.1
Derivatives (Level 1 measurement):
Foreign currency forward exchange contracts	0.5	0.0
Carrying Amount [Member] \| Derivatives (Level 1 Measurement) [Member] \| Interest Rate Swaps [Member]
Derivatives (Level 1 measurement):
Derivative asset	2.7	1.5
Carrying Amount [Member] \| Non-financial Assets and Liabilities (Level 3 Measurement) [Member]
Non-financial liabilities (Level 3 measurement):
Stock equivalent units	17.6	13.6
Fair Value [Member]
Non-derivatives:
Cash and cash equivalents	91.4	90.2
Non-derivatives:
Long-term debt (including current portion)	223.9	218.4
Finance leases (including current portion)	3.8	5.9
Fair Value [Member] \| Bank Overdrafts [Member]
Non-derivatives:
Bank overdraft	0.5	0.0
Fair Value [Member] \| Derivatives (Level 1 Measurement) [Member] \| Foreign Currency Forward Exchange Contracts [Member]
Derivatives (Level 1 measurement):
Derivative asset	0.0	1.1
Derivatives (Level 1 measurement):
Foreign currency forward exchange contracts	0.5	0.0
Fair Value [Member] \| Derivatives (Level 1 Measurement) [Member] \| Interest Rate Swaps [Member]
Derivatives (Level 1 measurement):
Derivative asset	2.7	1.5
Fair Value [Member] \| Non-financial Assets and Liabilities (Level 3 Measurement) [Member]
Non-financial liabilities (Level 3 measurement):
Stock equivalent units	$ 17.6	$ 13.6

Derivative liabilities.

No definition available.

Name:	iosp_DerivativesLiabilitiesAbstract
Namespace Prefix:	iosp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Finance leases fair value disclosure.

+ References

No definition available.

+ Details

Name:	iosp_FinanceLeasesFairValueDisclosure
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Non-derivatives assets.

+ References

No definition available.

+ Details

Name:	iosp_NonDerivativesAssetsAbstract
Namespace Prefix:	iosp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Non-derivatives liabilities.

+ References

No definition available.

+ Details

Name:	iosp_NonDerivativesLiabilitiesAbstract
Namespace Prefix:	iosp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Non-financial liabilities.

+ References

No definition available.

+ Details

Name:	iosp_NonFinancialLiabilitiesAbstract
Namespace Prefix:	iosp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Stock equivalent units fair value disclosure.

+ References

No definition available.

+ Details

Name:	iosp_StockEquivalentUnitsFairValueDisclosure
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other 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. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_DerivativeAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a 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. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: