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Stock-Based Compensation - Summary of Activity for Outstanding and Exercisable SARs (Detail) - Stock Appreciation Rights (SARs) [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock appreciation rights outstanding	282,907	599,334
Stock appreciation rights exercisable	221,375
Weighted Average Base Value, Stock appreciation rights outstanding	$ 28.62
Weighted Average Base Value, Stock appreciation rights exercisable	$ 27.92
Weighted Average Remaining Contractual Life, Stock appreciation rights outstanding	3 years 3 months 19 days
Weighted Average Remaining Contractual Life, Stock appreciation rights exercisable	3 years
Aggregate Intrinsic Value, Stock appreciation rights outstanding	$ 18,639
Aggregate Intrinsic Value, Stock appreciation rights exercisable	$ 14,740

X

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options exercisable.

+ References

No definition available.

+ Details

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options exercisable aggregate intrinsic value.

+ References

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options exercisable weighted average base value.

+ References

No definition available.

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- Definition

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+ References

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options outstanding weighted average base value.

+ References

No definition available.

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X

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

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- Definition

Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options.

+ References

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