Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Status of Supplemental Executive Retirement Plan (Detail)

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Employee Benefit Plans - Status of Supplemental Executive Retirement Plan (Detail) - Supplemental Employee Retirement Plans, Defined Benefit [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Change in projected benefit obligation:    
Obligation at beginning of year $ 11,233 $ 9,234
Service cost 1,711 1,590
Interest cost 448 383
Actuarial loss (gain) 429 295
Benefits paid (265) (269)
Obligation at end of year 13,556 11,233
Accumulated benefit obligation 10,204 8,557
Change in fair value of plan assets:    
Employer contributions 265 269
Benefits paid (265) (269)
Funded status recognized $ (13,556) $ (11,233)