Defined Benefit Pension Plan - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Postemployment Benefits [Abstract] | ||
| Service cost | $ 28 | $ 22 |
| Interest cost | 27 | 25 |
| Amortization | 24 | 22 |
| Net periodic benefit cost | $ 79 | $ 69 |