Retirement Plans and Related Post Retirement Benefits - Reconciliation of Beginning and Ending Balances of Projected Benefit Obligation (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| SERP | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Balance at beginning of the year | $ 21,533 | $ 20,418 | |
| Service Cost | 186 | 173 | $ 194 |
| Interest Cost | 897 | 901 | 843 |
| Actuarial (Gain) Loss | 2,873 | 389 | |
| Benefits Paid | (348) | (348) | |
| Balance at end of the year | 25,141 | 21,533 | 20,418 |
| SERP Medical | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Balance at beginning of the year | 1,021 | 925 | |
| Service Cost | 7 | 5 | 6 |
| Interest Cost | 41 | 40 | 39 |
| Actuarial (Gain) Loss | 307 | 112 | |
| Benefits Paid | (69) | (61) | |
| Balance at end of the year | $ 1,307 | $ 1,021 | $ 925 |
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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of 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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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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 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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- 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.
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