Property, Plant and Mine Development - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment
Impairment of Long-Lived Assets to be Disposed of	$ 1,100
Property Plant Equipment Interest Capitalization	500	$ 1,400	$ 500
Capital lease obligation	$ 0