Goodwill and Other Intangible Assets (Additional Information) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 16.5	$ 14.8	$ 11.2
Estimated future amortization expense for 2019	17.7
Estimated future amortization expense for 2020	14.6
Estimated future amortization expense for 2021	13.8
Estimated future amortization expense for 2022	13.3
Estimated future amortization expense for 2023	$ 12.7