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 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Inventory [Line Items]          
Percentage of metal component in inventory 68.00%   68.00%   65.00%
Adjustment decrease to cost of sales $ 0.2 $ (0.7) $ 1.1 $ 0.1  
Inventories at period end 235.9   235.9   $ 208.1
Excess of market over reported value 102.0   102.0   121.0
Estimate of Fair Value Measurement [Member]          
Inventory [Line Items]          
Inventories at period end $ 337.9   $ 337.9   $ 329.1