Property, Plant and Equipment, Net - Property, Plant and Equipment Details (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	$ 457,774	$ 439,681
Accumulated depreciation	(167,104)	(145,678)
Property, plant and equipment, net	290,670	294,003
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	13,187	13,187
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	115,422	114,051
Plant machinery
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	284,151	281,786
Mobile equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	12,828	10,366
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	$ 32,186	$ 20,291