Employee Benefit Plans - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) CompensationPlan	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Aggregate deferred under Compensation Plan	$ 2.4	$ 2.3
Number of incentive compensation plans | CompensationPlan	3
Earnings before tax upon achieving a specified earnings threshold	8.25%
Accrued Incentive Compensation expense	$ 1.6	3.0	$ 11.7
Percentage of employee compensation contribution	6.00%
Percentage of vesting contribution	25.00%
Vesting period of employees	5 years
Matching contribution of employees	$ 10.1	11.8	11.5
Safety Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Compensation expense related to incentive plans	$ 0.9	$ 0.9	$ 1.0