Retirement Plans - Schedule of Impact of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates (Detail) $ in Thousands |
12 Months Ended |
---|---|
Dec. 31, 2017
USD ($)
| |
Retirement Benefits [Abstract] | |
Effect on total of service and interest cost components, One-Percentage-Point Increase | $ 29 |
Effect on postretirement benefit obligation, One-Percentage-Point Increase | 2 |
Effect on total of service and interest cost components, One-Percentage-Point Decrease | (27) |
Effect on postretirement benefit obligation, One-Percentage-Point Decrease | $ (2) |