Summary of Significant Accounting Policies - Computation of Depreciation of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2014
Buildings and improvements | Minimum
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property Plant And Equipment [Line Items]
Property and equipment useful life	10 years
Buildings and improvements | Maximum
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property Plant And Equipment [Line Items]
Property and equipment useful life	40 years
Machinery and equipment | Minimum
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property Plant And Equipment [Line Items]
Property and equipment useful life	3 years
Machinery and equipment | Maximum
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property Plant And Equipment [Line Items]
Property and equipment useful life	20 years
Mine development costs
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property Plant And Equipment [Line Items]
Property and equipment useful life	Units-of-production
Landfill disposal costs
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property Plant And Equipment [Line Items]
Property and equipment useful life	Units-of-consumption