Quarterly report pursuant to Section 13 or 15(d)

Property, Plant and Equipment - Additional Information (Detail)

v3.10.0.1
Property, Plant and Equipment - Additional Information (Detail)
$ in Millions
 1 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
May 31, 2018
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2018
license
Property, Plant and Equipment [Line Items]        
Write-off of non-producing acreage $ 2.7      
Cash consideration from transfer of permit   $ 0.2    
Decrease in liabilities from transfer of permit   $ 1.3    
Loss on transfer of permit     $ 1.0  
United Kingdom        
Property, Plant and Equipment [Line Items]        
Number of non-operating interest in licenses | license       2