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Debt - Narrative (Details) - USD ($)
3 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Jun. 30, 2019
Debt Instrument [Line Items]      
Short-term borrowings $ 77,600,000   $ 19,700,000
Interest costs 7,400,000 $ 7,200,000  
Interest costs, capitalized 2,000,000.0 $ 900,000  
Credit Agreement      
Debt Instrument [Line Items]      
Maximum borrowing capacity 400,000,000.0    
Letters of credit issued 5,900,000    
Short-term borrowings 77,600,000    
Credit Agreement available for future borrowings $ 316,500,000    
Credit Agreement | LIBOR      
Debt Instrument [Line Items]      
Interest rate margin 1.25%    
Credit Agreement | LIBOR | Minimum      
Debt Instrument [Line Items]      
Interest rate margin 1.00%    
Credit Agreement | LIBOR | Maximum      
Debt Instrument [Line Items]      
Interest rate margin 1.75%    
Credit Agreement | Base Rate      
Debt Instrument [Line Items]      
Interest rate margin 0.25%    
Credit Agreement | Base Rate | Minimum      
Debt Instrument [Line Items]      
Interest rate margin 0.00%    
Credit Agreement | Base Rate | Maximum      
Debt Instrument [Line Items]      
Interest rate margin 0.75%    
Letters of credit      
Debt Instrument [Line Items]      
Commitment fee rate 0.20%    
Letter of credit fees 1.25%    
Required interest coverage ratio 3.50    
Letters of credit | Minimum      
Debt Instrument [Line Items]      
Commitment fee rate 0.125%    
Letter of credit fees 1.00%    
Letters of credit | Maximum      
Debt Instrument [Line Items]      
Commitment fee rate 0.40%    
Letter of credit fees 1.75%    
Required debt to capital ratio (less than) 0.55    
Revolving Credit Facility | Unsecured Revolving Credit Facility, Credit Agreement      
Debt Instrument [Line Items]      
Borrowing rate 3.30%