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Other Financial Statement Information - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 01, 2018
Nov. 02, 2016
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Inventory Disclosure [Abstract]              
Cost of inventories for certain materials using LIFO method     $ 25.8   $ 25.8   $ 25.1
Expense (benefit) charge to earnings from LIFO inventory changes     $ 0.6 $ 0.1 $ 1.1 $ 0.2  
Name of plaintiff         Altalink, L.P.    
Complaint filling date         November 2016    
Estimated damages from defendants $ 29.4 $ 56.0