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Property, Plant and Equipment, net - Narrative (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Property, Plant and Equipment [Line Items]      
Depreciation expenses $ 17,117,000 $ 7,267,000 $ 6,441,000
Depletion expense 47,000 33,000 3,000
Construction in progress      
Property, Plant and Equipment [Line Items]      
Interest expense capitalized $ 0 $ 0 $ 139,000