Annual report pursuant to Section 13 and 15(d)

Derivative Contracts - Effects of Derivative Contracts in Condensed Consolidated Financial Statements (Detail)

v3.10.0.1
Derivative Contracts - Effects of Derivative Contracts in Condensed Consolidated Financial Statements (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]      
Gross Amounts of Recognized Assets $ 3.5 $ 5.3  
Gross Amounts Offset in Consolidated Balance Sheet (3.5) (3.2)  
Net Amounts of Assets Presented in Consolidated Balance Sheet 0.0 2.1  
Consolidated balance sheet location:      
Derivative contract assets, current 0.0 2.0  
Derivative Asset, Noncurrent   0.1  
Derivative contract liabilities, current 0.9 0.2  
Derivative contract liabilities, noncurrent 2.1 0.2  
Gross Amounts of Recognized Liabilities 6.5 3.6  
Gross Amounts Offset in Consolidated Balance Sheet (3.5) (3.2)  
Net Amounts of Liabilities Presented in Consolidated Balance Sheet 3.0 0.4  
Cost of Sales [Member]      
Derivative losses (gains) income statement location      
Losses (Gains) on Derivatives 0.1 (3.4) $ (3.7)
Interest Rate Swap [Member]      
Consolidated balance sheet location:      
Gross Amounts of Recognized Liabilities 2.0    
Gross Amounts Offset in Consolidated Balance Sheet 0.0    
Net Amounts of Liabilities Presented in Consolidated Balance Sheet 2.0    
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax (1.5) 0.0  
Interest Rate Swap [Member] | Other Comprehensive Income (Loss) [Member]      
Derivative losses (gains) income statement location      
Losses (Gains) on Derivatives 2.0 0.0 0.0
Metal [Member]      
Derivatives, Fair Value [Line Items]      
Gross Amounts of Recognized Assets 3.3 5.3  
Gross Amounts Offset in Consolidated Balance Sheet (3.3) (3.2)  
Net Amounts of Assets Presented in Consolidated Balance Sheet 0.0 2.1  
Consolidated balance sheet location:      
Gross Amounts of Recognized Liabilities 4.2 3.3  
Gross Amounts Offset in Consolidated Balance Sheet (3.4) (3.2)  
Net Amounts of Liabilities Presented in Consolidated Balance Sheet 0.8 0.1  
Metal [Member] | Cost of Sales [Member]      
Derivative losses (gains) income statement location      
Losses (Gains) on Derivatives 0.3 (4.0) (3.6)
Energy Related Derivative [Member]      
Derivatives, Fair Value [Line Items]      
Gross Amounts of Recognized Assets 0.1 0.0  
Gross Amounts Offset in Consolidated Balance Sheet (0.1) 0.0  
Net Amounts of Assets Presented in Consolidated Balance Sheet 0.0 0.0  
Consolidated balance sheet location:      
Gross Amounts of Recognized Liabilities 0.3 0.3  
Gross Amounts Offset in Consolidated Balance Sheet (0.1) 0.0  
Net Amounts of Liabilities Presented in Consolidated Balance Sheet 0.2 0.3  
Energy Related Derivative [Member] | Cost of Sales [Member]      
Derivative losses (gains) income statement location      
Losses (Gains) on Derivatives (0.2) $ 0.6 $ (0.1)
Collateral On Deposit [Member]      
Derivatives, Fair Value [Line Items]      
Gross Amounts of Recognized Assets 0.1    
Gross Amounts Offset in Consolidated Balance Sheet (0.1)    
Net Amounts of Assets Presented in Consolidated Balance Sheet $ 0.0