Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands |
3 Months Ended | ||
---|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
Dec. 31, 2017 |
|
Property, Plant and Equipment [Line Items] | |||
Gross property and equipment | $ 20,206 | $ 15,636 | |
Depreciation expense | 156 | $ 133 | |
Asset Under Construction [Member] | |||
Property, Plant and Equipment [Line Items] | |||
Gross property and equipment | 7,988 | 3,671 | |
Assets Under Construction Held Under Finance Lease [Member] | |||
Property, Plant and Equipment [Line Items] | |||
Gross property and equipment | $ 7,600 | $ 3,100 |