Quarterly report pursuant to Section 13 or 15(d)

Debt (Narrative) (Detail)

v3.5.0.2
Debt (Narrative) (Detail)
$ in Millions
 9 Months Ended 18 Months Ended
Dec. 31, 2016
Sep. 30, 2016
USD ($)
Jun. 30, 2018
Jun. 30, 2016
USD ($)
Line Of Credit Facility [Line Items]        
Credit facility borrowing base   $ 20.0   $ 20.0
Debt service coverage ratio minimum at each quarter   1.2    
Notes Payable, Fair Value Disclosure   $ 15.0    
Commitment fee percentage   2.30%    
Maximum [Member]        
Line Of Credit Facility [Line Items]        
Ratio of net debt to EBITDAX 5.0      
Maximum [Member] | Scenario, Forecast [Member]        
Line Of Credit Facility [Line Items]        
Ratio of net debt to EBITDAX     3.0  
Senior Tranche [Member]        
Line Of Credit Facility [Line Items]        
Debt instrument, commitment fee   1.50%    
Line Of Credit Facility Maximum Borrowing Capacity   $ 50.0    
Subordinated Tranche [Member]        
Line Of Credit Facility [Line Items]        
Debt instrument, commitment fee   2.30%    
Line Of Credit Facility Maximum Borrowing Capacity   $ 15.0    
Additional Term Loan Available Until Dec. 31, 2016 [Member]        
Line Of Credit Facility [Line Items]        
Notes Payable to Bank   $ 5.0    
Term Loan [Member]        
Line Of Credit Facility [Line Items]        
Debt instrument interest rate spread   5.75%    
Notes Payable to Bank   $ 15.0