Pension Plans - Weighted-Average Asset Allocations of Plan Assets (Detail) |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Defined Benefit Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations of pension plan assets | 100.00% | 100.00% |
| Equity Securities [Member] | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations of pension plan assets | 61.00% | 61.00% |
| Debt Securities [Member] | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations of pension plan assets | 35.00% | 37.00% |
| Cash and Equivalents [Member] | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations of pension plan assets | 4.00% | 2.00% |