| Shareholders' Equity - Components of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands | 12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | |
| Accumulated Other Comprehensive Income (Loss) [Line Items] | |||
| Other Comprehensive (Loss) Income | $ 2,142 | $ (430) | $ (3,115) | 
| Foreign Currency Translation Adjustments | |||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | |||
| Other Comprehensive (Loss) Income | 4,132 | (626) | (4,617) | 
| Retirement Liability Adjustment | |||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | |||
| Other Comprehensive (Loss) Income | (1,990) | 196 | 1,502 | 
| Other Comprehensive (Loss) Income, Before Tax | (2,377) | 301 | 2,311 | 
| Tax Benefit (Expense) | $ 387 | $ (105) | $ (809) | 
| X | ||||||||||
| 
- 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. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount before tax of other comprehensive income (loss) attributable to parent entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Amount after tax of other comprehensive income (loss) attributable to parent entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 |