Fair Value Measurements - Carrying Amount and Fair Values of the Company's Assets and Liabilities Measured on a Recurring Basis (Detail) - Recurring [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Carrying Amount [Member]
Non-derivatives:
Cash and cash equivalents	$ 117.0	$ 105.3
Non-derivatives:
Finance leases (including current portion)	0.4	0.6
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign Currency Forward Exchange Contracts [Member]
Derivatives (Level 1 measurement):
Foreign currency forward exchange contracts	1.9	0.0
Derivatives (Level 1 measurement):
Foreign currency forward exchange contracts	0.0	0.5
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Non-financial liabilities (Level 3 measurement):
Stock equivalent units	20.8	17.2
Fair Value [Member]
Non-derivatives:
Cash and cash equivalents	117.0	105.3
Non-derivatives:
Finance leases (including current portion)	0.4	0.6
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign Currency Forward Exchange Contracts [Member]
Derivatives (Level 1 measurement):
Foreign currency forward exchange contracts	1.9	0.0
Derivatives (Level 1 measurement):
Foreign currency forward exchange contracts	0.0	0.5
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Non-financial liabilities (Level 3 measurement):
Stock equivalent units	$ 20.8	$ 17.2