Annual report pursuant to Section 13 and 15(d)

Property and Equipment - Additional Information (Detail)

v3.8.0.1
Property and Equipment - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property, Plant and Equipment [Line Items]      
Gross property and equipment $ 15,636 $ 11,726  
Depreciation expense 551 345 $ 147
Asset Under Construction [Member]      
Property, Plant and Equipment [Line Items]      
Gross property and equipment $ 3,671 $ 37