Stock Options and Other Equity-Based Incentive Instruments - Information about Options (Detail) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Information about Options
Intrinsic value of options exercised	$ 3,483,000	$ 969,000	$ 1,209,000
Fair value of options that vested	580,000	734,000	965,000
Total compensation costs for options recognized in income	580,000	734,000	965,000
Total tax benefit recognized in income related to compensation costs for options	$ 244,000	$ 380,000	$ 378,000
Weighted average fair value of grants (per option)			$ 8.17

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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No definition available.

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

+ References

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-Publisher FASB
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