Retirement Plans and Related Post Retirement Benefits - Summarizes the Components of the Net Periodic Cost (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| SERP | |||
| Net Periodic Cost | |||
| Service Cost — Benefits Earned During Period | $ 186 | $ 173 | $ 194 |
| Interest Cost | 897 | 901 | 843 |
| Amortization of Prior Service Cost | 387 | 413 | 495 |
| Amortization of Losses | 369 | 343 | 449 |
| Net Periodic Cost | 1,839 | 1,830 | 1,981 |
| SERP Medical | |||
| Net Periodic Cost | |||
| Service Cost — Benefits Earned During Period | 7 | 5 | 6 |
| Interest Cost | 41 | 40 | 39 |
| Amortization of Prior Service Cost | 16 | 24 | 26 |
| Amortization of Losses | 31 | 22 | 26 |
| Net Periodic Cost | $ 95 | $ 91 | $ 97 |
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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