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Long-Term Debt - Senior Secured Credit Facility - Additional Information (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Nov. 30, 2018
Jul. 31, 2015
Debt Instrument [Line Items]        
Senior Secured Credit Facility $ 194,000,000 $ 183,000,000    
Senior Secured Credit Facility        
Debt Instrument [Line Items]        
Weighted average interest rate on borrowings 4.85%      
Debt instrument borrowing base $ 80,500,000      
Senior secured credit facility sub limit 2,500,000      
Debt instrument expanded borrowing base $ 275,000,000      
Senior Secured Credit Facility | Minimum        
Debt Instrument [Line Items]        
Debt instrument expanded borrowing base     $ 190,000,000  
Commitment fee percentage 0.375%      
Senior Secured Credit Facility | Maximum        
Debt Instrument [Line Items]        
Debt instrument expanded borrowing base     $ 275,000,000  
Commitment fee percentage 0.50%      
LRAI | Citibank N A | Senior Secured Credit Facility        
Debt Instrument [Line Items]        
Debt instrument face amount       $ 500,000,000
Letter of Credit | Senior Secured Credit Facility        
Debt Instrument [Line Items]        
Debt instrument borrowing base $ 500,000