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Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Detail)
12 Months Ended
Dec. 31, 2016
Buildings and improvements | Minimum  
Property Plant And Equipment [Line Items]  
Property plant and equipment useful life 10 years
Buildings and improvements | Maximum  
Property Plant And Equipment [Line Items]  
Property plant and equipment useful life 40 years
Machinery and equipment | Minimum  
Property Plant And Equipment [Line Items]  
Property plant and equipment useful life 3 years
Machinery and equipment | Maximum  
Property Plant And Equipment [Line Items]  
Property plant and equipment useful life 20 years
Mine development costs  
Property Plant And Equipment [Line Items]  
Mine development costs units-of-production