Long-Term Debt - Long-Term Debt Instrument (Additional Information) (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		0.81%
5.660% senior notes, Series C, semi-annual interest payments, balloon due 2016
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.50%	4.50%
4.500% senior notes, Series E, quarterly interest payments, balloon due 2018
Debt Instrument [Line Items]
Debt instrument maturity year	2018	2018
4.200% senior notes, semi-annual interest payments, balloon due 2024
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.20%	4.20%
Debt instrument maturity year	2024	2024
5-year term loan facility, periodic interest and principal payments, LIBOR plus up to 1.750%, expires June 28, 2022
Debt Instrument [Line Items]
Line of credit facility, expiration period	5 years	5 years
Line of credit facility, expiration date	Jun. 28, 2022	May 20, 2019
5-year term loan facility, periodic interest and principal payments, LIBOR plus up to 1.750%, expires June 28, 2022 \| LIBOR
Debt Instrument [Line Items]
Debt instrument, variable interest rate	1.75%	1.75%
5-year revolving loan facility, periodic interest payments, currently LIBOR plus up to 1.500%, plus commitment fees up to 0.250%, expires June 28, 2022
Debt Instrument [Line Items]
Line of credit facility, expiration period	5 years	5 years
Line of credit facility, commitment fee percentage	0.25%	0.25%
Line of credit facility, expiration date	Jun. 28, 2022	May 20, 2019
5-year revolving loan facility, periodic interest payments, currently LIBOR plus up to 1.500%, plus commitment fees up to 0.250%, expires June 28, 2022 \| LIBOR
Debt Instrument [Line Items]
Debt instrument, variable interest rate	1.50%	1.50%

Debt Instruments Maturity Year

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- 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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- 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

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- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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