Pensions and Other Post-retirement Benefits - Additional Information (Detail) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 31, 2014 Employee
Defined Benefit Plan Disclosure [Line Items]
Percentage match of the first one percent of contributions made by participating employees		100.00%
Percentage Match Of The Next Five Percent Of Contributions Made By Participating Employees		50.00%
Medical and life insurance maximum participant coverage age, in years		65 years
Number of former employees who get elected to participate in a lump sum pension benefits payment | Employee				2,700
Benefits paid	$ 50.0
Other comprehensive (gain) loss as a result of after tax adjustments for additional minimum pension liability		$ 1.0	$ 1.6
Target allocation to equity managers, minimum		45.00%
Target allocation to equity managers maximum		55.00%
Ten Year Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Number of historical years for which compounded annualized returns is considered		10 years
Compounded annualized return of pension plan		6.10%
Twenty Five Year Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Number of historical years for which compounded annualized returns is considered		25 years
Compounded annualized return of pension plan		9.50%
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Benefits paid		$ 60.2	116.1
Estimated net actuarial gain that will be amortized from accumulated other comprehensive loss into net periodic benefit cost		16.7
Estimated net prior service cost that will be amortized from accumulated other comprehensive loss into net periodic benefit cost		(1.1)
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefits paid		0.7	$ 1.3
Estimated net actuarial gain that will be amortized from accumulated other comprehensive loss into net periodic benefit cost		0.2
Estimated net prior service cost that will be amortized from accumulated other comprehensive loss into net periodic benefit cost		$ (0.4)