Retirement Benefits - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) employee	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for all defined benefit pension plans	$ 150.4	$ 163.3
Percentage of excess gains and losses over benefit obligation or market value of assets amortized	10.00%
Costs of defined contribution plans	$ 10.3	9.1	$ 8.4
Number of participants covering under multi employer pension plan | employee	398
Costs of bargaining unit-sponsored multi-employer plans and defined contribution plans	$ 1.0	$ 1.0	$ 1.1
Weighted average annual rate of increase in the per capita cost of covered health care benefits assumed	6.94%
Assumed decrease of weighted average health care cost trend rate	4.50%
Year that reaches assumed decrease of weighted average health care cost trend rate	2027
Increase in service and interest cost components of the net periodic benefit cost, as 1% increase in health care cost trend rates	$ 0.2
Increase in accumulated postretirement benefit obligation, as 1% increase in health care cost trend rates	1.6
Decrease in service and interest cost components of the net periodic benefit cost, as 1% decrease in health care cost trend rates	0.1
Decrease in accumulated postretirement benefit obligation, as 1% decrease in health care cost trend rates	1.3
Future estimated benefit payments for year 2016	14.2
Future estimated benefit payments for year 2017	10.0
Future estimated benefit payments for year 2018	10.6
Future estimated benefit payments for year 2019	10.3
Future estimated benefit payments for year 2020	10.6
Future estimated benefit payments for years 2021 to 2025	52.6
Defined Contribution Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, expected contribution for next fiscal year	20.8
401k
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, expected contribution for next fiscal year	8.1
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contribution for next fiscal year	6.1
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contribution for next fiscal year	$ 0.9
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities, minimum	40.00%
Target allocation of fund assets in equities, maximum	60.00%
Target allocation of fund assets in equities	50.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities, minimum	40.00%
Target allocation of fund assets in equities, maximum	60.00%
Target allocation of fund assets in equities	50.00%