Common Stock and Share-Based Compensation - Stock Units Grants and Stock Units Expense (Detail) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of RSUs vested/distributed during the period	$ 7,960	$ 8,920	$ 7,958
Weighted-average grant date fair value of RSUs granted (USD per share)	$ 17.91	$ 19.13	$ 16.41
Tax benefit related to RSU expense	$ 2,071	$ 1,694	$ 2,303

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ 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)(iii)(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.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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