| **Share-Based Compensation - Components of Share Based Compensation Awards (Detail) (USD $)In Thousands, unless otherwise specified** | 12 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------------|-----------------|
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| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                                                    |            |   |   |
| Pre-tax compensation expense                                                                                                          | $ 1,773         | $ 1,492 | $ 1,315 |
| Income tax benefit                                                                                                                    | (547)           | (451) | (392) |
| Total share-based compensation expense, net of income taxes                                                                           | 1,226           | 1,041 | 923 |
| Stock and ESPP Options                                                                                                                |            |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                                                    |            |   |   |
| Pre-tax compensation expense                                                                                                          | 253             | 284 | 237 |
| Income tax benefit                                                                                                                    | (16)            | (23) | (21) |
| Total share-based compensation expense, net of income taxes                                                                           | 237             | 261 | 216 |
| Restricted Stock Awards                                                                                                               |            |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                                                    |            |   |   |
| Pre-tax compensation expense                                                                                                          | 1,520           | 1,208 | 1,078 |
| Income tax benefit                                                                                                                    | (531)           | (428) | (371) |
| Total share-based compensation expense, net of income taxes                                                                           | $ 989           | $ 780 | $ 707 |

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| - 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.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901Reference 2: 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=d3e301413-122809Reference 3: 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=6415400&loc=d3e5070-113901Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F
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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.
+ 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.
+ 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 (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901
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| X                                                                                                                                                                                                      |
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