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Long-Term Debt - Senior Secured Credit Facility - Additional Information (Details) - USD ($)
6 Months Ended
Jun. 30, 2019
Jun. 01, 2019
May 31, 2019
Dec. 31, 2018
Jul. 31, 2015
Debt Instrument [Line Items]          
Senior Secured Credit Facility $ 205,000,000     $ 183,000,000  
Senior Secured Credit Facility          
Debt Instrument [Line Items]          
Weighted average interest rate on borrowings 5.49%        
Debt instrument borrowing base $ 84,500,000        
Senior secured credit facility sub limit 2,500,000        
Debt instrument expanded borrowing base $ 290,000,000        
Senior Secured Credit Facility | Minimum          
Debt Instrument [Line Items]          
Commitment fee percentage 0.375%        
Debt instrument expanded borrowing base     $ 275,000,000    
Senior Secured Credit Facility | Maximum          
Debt Instrument [Line Items]          
Commitment fee percentage 0.50%        
Debt instrument expanded borrowing base   $ 290,000,000      
Letter of Credit | Senior Secured Credit Facility          
Debt Instrument [Line Items]          
Debt instrument borrowing base $ 500,000        
LRAI | Citibank N A | Senior Secured Credit Facility          
Debt Instrument [Line Items]          
Debt instrument face amount         $ 500,000,000