Retirement Plans and Other Post-Retirement Benefits - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Age	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan retired union employees eligible age to participate in health care benefit plan | Age	55
Defined benefit plan retired union employees eligible service period	5 years
Accumulated benefit obligation for all defined benefit pension plans	$ 584.3	$ 537.6
Defined contribution plans Employees contribution	50.00%
Expense associated with Defined Contribution Plans	$ 2.3	2.0	$ 2.1
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge		7.3
Pension settlement charge settled		$ 24.2
Discount rates	3.85%	4.43%
Prior service cost as a component of net periodic benefit cost from accumulated other comprehensive income (loss)	$ 3.1
Actuarial net (gain) loss as a component of net periodic benefit cost from accumulated other comprehensive income (loss)	$ 0.2
Pension Benefits [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	1.90%
Pension Benefits [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	4.55%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	3.68%	4.18%
Prior service cost as a component of net periodic benefit cost from accumulated other comprehensive income (loss)		$ 13.5
Actuarial net (gain) loss as a component of net periodic benefit cost from accumulated other comprehensive income (loss)		$ 0.3
Other Benefits [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	4.02%
Other Benefits [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	4.21%