Property, Plant and Mine Development - Schedule of Property, Plant and Mine Development (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment
Property Plant Equipment Interest Capitalization	$ 500	$ 1,400	$ 500
Property, plant and mine development	770,585	722,511
Accumulated depletion, depreciation and amortization	(209,389)	(156,756)
Total property, plant and mine development, net	561,196	565,755
Mining property and mine development
Property, Plant and Equipment
Property, plant and mine development	222,439	197,824
Asset retirement cost
Property, Plant and Equipment
Property, plant and mine development	9,889	9,559
Land
Property, Plant and Equipment
Property, plant and mine development	30,322	28,443
Land improvements
Property, Plant and Equipment
Property, plant and mine development	37,791	35,322
Buildings
Property, Plant and Equipment
Property, plant and mine development	51,280	47,149
Machinery and equipment
Property, Plant and Equipment
Property, plant and mine development	360,817	323,618
Furniture and fixtures
Property, Plant and Equipment
Property, plant and mine development	1,917	1,599
Construction-in-progress
Property, Plant and Equipment
Property, plant and mine development	$ 56,130	$ 78,997