Quarterly report pursuant to Section 13 or 15(d)

Property, Plant and Equipment - Additional Information (Detail)

v3.8.0.1
Property, Plant and Equipment - Additional Information (Detail)
1 Months Ended 3 Months Ended 9 Months Ended
Feb. 28, 2017
USD ($)
License
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Property, Plant and Equipment [Line Items]          
Depletion   $ 0   $ 0  
Asset purchase $ 85,100,000        
Number of operated producing wells 19        
Development Expenses          
Property, Plant and Equipment [Line Items]          
Depreciation expense   92,000 $ 31,000 231,000 $ 55,000
Australia          
Property, Plant and Equipment [Line Items]          
Reserves   $ 0   $ 0  
United Kingdom          
Property, Plant and Equipment [Line Items]          
Number of non-operating interest in licenses | License 2