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Long-term Debt (Schedule Of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Outstanding borrowings	$ 373,541us-gaap_LongTermDebt	$ 363,526us-gaap_LongTermDebt
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding borrowings	24,000us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = us-gaap_DomesticLineOfCreditMember	14,000us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = us-gaap_DomesticLineOfCreditMember
Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding borrowings	$ 349,541us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember	$ 349,526us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
Senior notes, interest rate	4.10%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
Debt instruments, maturity date	2022

X

- Definition

Debt instruments maturity date.

+ References

No definition available.

+ Details

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Namespace Prefix:	neu_
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Balance Type:	na
Period Type:	duration

X

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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X

- Details

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Period Type:	duration

X

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

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

X

- Details

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Namespace Prefix:
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X

- Details

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