Annual report pursuant to Section 13 and 15(d)

Share-based Compensation - Summary of Share-based Compensation Expense (Detail)

v3.10.0.1
Share-based Compensation - Summary of Share-based Compensation Expense (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 6.7 $ 8.2 $ 6.9
Net tax benefit related to share-based compensation expense 1.2 3.2 2.6
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense 0.5 1.2 1.3
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense 3.2 3.0 2.4
Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 3.0 $ 4.0 $ 3.2