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Long-Term Debt - Additional Information 1 (Detail) - Bank Credit Facility - USD ($)
$ in Millions
3 Months Ended
Jul. 16, 2019
Aug. 14, 2018
Dec. 31, 2019
Sep. 30, 2019
Debt Instrument [Line Items]        
Maturity of credit facility Jul. 16, 2024      
Bank credit facility $ 1,575.0      
Committed borrowing base $ 1,500.0      
Borrowings outstanding       $ 1,265.0
Scenario Forecast        
Debt Instrument [Line Items]        
Leverage ratio     400.00%  
Current ratio     100.00%  
Minimum        
Debt Instrument [Line Items]        
Commitment fee on unused borrowing base   0.375%    
Maximum        
Debt Instrument [Line Items]        
Commitment fee on unused borrowing base   0.50%    
LIBOR | Minimum        
Debt Instrument [Line Items]        
Spread rate for interest rate on credit facility   1.75%    
LIBOR | Maximum        
Debt Instrument [Line Items]        
Spread rate for interest rate on credit facility   2.75%    
Base Rate | Minimum        
Debt Instrument [Line Items]        
Spread rate for interest rate on credit facility   0.75%    
Base Rate | Maximum        
Debt Instrument [Line Items]        
Spread rate for interest rate on credit facility   1.75%