Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Detail) |
12 Months Ended |
|---|---|
Dec. 31, 2015 | |
| Building and improvements | Minimum | |
| Property Plant And Equipment Estimated Useful Life [Line Items] | |
| Property plant and equipment useful life | 10 years |
| Building and improvements | Maximum | |
| Property Plant And Equipment Estimated Useful Life [Line Items] | |
| Property plant and equipment useful life | 40 years |
| Machinery and equipment | Minimum | |
| Property Plant And Equipment Estimated Useful Life [Line Items] | |
| Property plant and equipment useful life | 3 years |
| Machinery and equipment | Maximum | |
| Property Plant And Equipment Estimated Useful Life [Line Items] | |
| Property plant and equipment useful life | 20 years |
| Mine development costs | |
| Property Plant And Equipment Estimated Useful Life [Line Items] | |
| Mine development costs | units-of-production |