Employee Benefit Plans - Additional Information (Detail) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2015
USD ($)
CompensationPlan
|
Dec. 31, 2014
USD ($)
|
Dec. 31, 2013
USD ($)
|
|
| Defined Benefit Plan Disclosure [Line Items] | |||
| Aggregate deferred under Compensation Plan | $ 2.3 | $ 2.4 | |
| Number of incentive compensation plans | CompensationPlan | 3 | ||
| Earnings before tax upon achieving a specified earnings threshold | 8.25% | ||
| Accrued Incentive Compensation expense | $ 3.0 | 11.7 | $ 11.5 |
| Compensation expense related to incentive plans | $ 5.8 | 4.8 | 2.4 |
| Percentage of employee compensation contribution | 6.00% | ||
| Percentage of vesting contribution | 25.00% | ||
| Vesting period of employees | 5 years | ||
| Matching contribution of employees | $ 11.8 | 11.5 | 10.5 |
| Safety Incentive Plan [Member] | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Compensation expense related to incentive plans | $ 0.9 | $ 1.0 | $ 1.0 |