Retirement Plans - Components of Estimated Net Pension Plan Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Net pension income	$ (0.5)	$ (0.5)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost	2.2	2.8
Expected return on assets	(3.5)	(3.7)
Amortization, net	0.8	0.4
Net pension income	$ (0.5)	$ (0.5)