Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Additional Information (Detail)

v3.8.0.1
Share-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 9.8 $ 11.3  
Unrecognized compensation cost on non-vested stock awards $ 80.9    
Unrecognized compensation cost on non-vested stock awards, weighted-average period of recognition 1 year 4 months 24 days    
Weighted-average grant date fair value of SARs granted $ 86.30    
Total vesting date fair value of stock units $ 0.1 $ 0.1  
SARs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
SARs granted 0    
Weighted-average grant date fair value of SARs granted     $ 28.32
Total intrinsic value of awards exercised for SARs $ 122.2   $ 16.8