Lease Commitments - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Lessee, operating lease, lease not yet commenced, liability				$ 40.1
Net rental expense	$ 79.0	$ 76.7	$ 76.1
Upper Limit
Lessee, Lease, Description [Line Items]
Lease terms (in years)				15 years
Lower Limit
Lessee, Lease, Description [Line Items]
Lease terms (in years)				9 years