Pensions and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Postemployment Benefits [Abstract]
Service cost	$ 0.5	$ 0.5
Interest cost	1.8	2.4
Expected return on plan assets	(2.1)	(2.5)
Amortization of net loss	0.4	0.5
Net periodic benefit cost	0.6	0.9
Defined contribution plan expense	$ 2.0	$ 2.2