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Asset Retirement Obligation - Additional Information (Detail) - USD ($)
$ in Thousands
Sep. 30, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]        
Post closure reclamation and site restoration obligation $ 1,234 $ 1,180 $ 1,765 $ 204