v3.7.0.1
Acquisitions - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Sep. 02, 2016
Jun. 02, 2014
Dec. 31, 2016
Dec. 31, 2014
Business Acquisition [Line Items]        
Allocation of purchase price, receivables   $ 120.2    
Allocation of purchase price, inventory   40.1    
Allocation of purchase price , property, plant and equipment   208.5    
Allocation of purchase price, assumed liabilities   190.3    
Purchase price of acquisition   $ 829.7    
ASP Grede Intermediate Holdings LLC [Member]        
Business Acquisition [Line Items]        
Equity ownership percentage   97.10% 100.00%  
Allocation of purchase price, inventory   $ 40.1    
Allocation of purchase price , property, plant and equipment   208.5    
Purchase price of acquisition   829.7    
Fair value gain on inventories       $ 4.4
Weighted average discount rate       4.04%
Business combination, transaction costs   $ 13.0    
ASP Grede Intermediate Holdings LLC [Member] | Customer Relationships and Platforms [Member]        
Business Acquisition [Line Items]        
Intangible assets, remaining useful life   10 years 10 years  
ASP Grede Intermediate Holdings LLC [Member] | Trade Names [Member]        
Business Acquisition [Line Items]        
Intangible assets, remaining useful life   15 years 15 years  
ASP Grede Intermediate Holdings LLC [Member] | Affiliates Of American Security [Member]        
Business Acquisition [Line Items]        
Purchase price, equity contributions   $ 251.1    
ASP Grede Intermediate Holdings LLC [Member] | Management [Member]        
Business Acquisition [Line Items]        
Purchase price, equity contributions   6.5    
ASP Grede Intermediate Holdings LLC [Member] | Investor [Member]        
Business Acquisition [Line Items]        
Purchase price, equity contributions   1.0    
ASP Grede Intermediate Holdings LLC [Member] | Related Parties [Member]        
Business Acquisition [Line Items]        
Business combination, transaction costs   $ 8.3    
ASP Grede Intermediate Holdings LLC [Member] | Brillion Iron Works, Inc. [Member]        
Business Acquisition [Line Items]        
Business acquisition date     Sep. 02, 2016  
Equity ownership percentage 100.00%      
Acquisition purchase price, cash consideration $ 14.0      
Allocation of purchase price, receivables 8.1      
Allocation of purchase price, inventory 3.8      
Allocation of purchase price , property, plant and equipment 15.9      
Allocation of purchase price, assumed liabilities $ 12.8      
ASP Grede Intermediate Holdings LLC [Member] | Brillion Iron Works, Inc. [Member] | Other Net [Member]        
Business Acquisition [Line Items]        
Gain on bargain purchase price     $ 1.0