Annual report pursuant to Section 13 and 15(d)

Retirement Plans and Related Post Retirement Benefits - Reconciliation of Beginning and Ending Balances of Projected Benefit Obligation (Detail)

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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, 2016
Dec. 31, 2015
Dec. 31, 2014
SERP      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Balance at beginning of the year $ 20,418 $ 20,990  
Service Cost 173 194 $ 247
Interest Cost 901 843 721
Actuarial (Gain) Loss 389 (1,261)  
Benefits Paid (348) (348)  
Balance at end of the year 21,533 20,418 20,990
SERP Medical      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Balance at beginning of the year 925 990  
Service Cost 5 6 3
Interest Cost 40 39 31
Actuarial (Gain) Loss 112 (54)  
Benefits Paid (61) (56)  
Balance at end of the year $ 1,021 $ 925 $ 990