Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment additions			$ 25,979		$ 10,464
Depreciation expense	$ 566	$ 338	968	$ 674
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Interest capitalized			169	0
Cost of Sales [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	157	82	259	161
General and Administrative Expense [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 30	$ 27	$ 59	$ 53