Stock Option and Purchase Plans - Compensation Expense Information Based on Fair Value of Stock Options (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | |||
| Stock Compensation Expense | $ 2,598 | $ 2,281 | $ 2,274 |
| Tax Benefit | (140) | (145) | (177) |
| Stock Compensation Expense, Net of Tax | $ 2,458 | $ 2,136 | $ 2,097 |
| X | ||||||||||
- Definition 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
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| X | ||||||||||
- Definition The amount of expense, net of income tax, 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. No definition available.
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition 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
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