Quarterly report pursuant to Section 13 or 15(d)

Inventories - Additional Information (Detail)

v3.10.0.1
Inventories - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Inventory [Line Items]          
Percentage of metal component in inventory 67.00%   67.00%   65.00%
Lower of cost or market (increase) decrease to cost of sales $ (1.2) $ 0.7 $ (0.1) $ 0.8  
Inventories at period end 218.8   218.8   $ 208.1
Excess of market over reported value 87.3   87.3   121.0
Estimate of Fair Value Measurement [Member]          
Inventory [Line Items]          
Inventories at period end $ 306.1   $ 306.1   $ 329.1