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Debt - Narrative (Details)
3 Months Ended
Sep. 30, 2016
USD ($)
Sep. 30, 2015
USD ($)
Debt Instrument [Line Items]    
Interest costs $ 7,500,000 $ 7,200,000
Interest costs, capitalized 200,000 $ 600,000
Credit Agreement    
Debt Instrument [Line Items]    
Maximum borrowing capacity 500,000,000  
Letters of credit issued 5,800,000  
Credit Agreement available for future borrowings $ 494,200,000  
Credit Agreement | LIBOR    
Debt Instrument [Line Items]    
Variable rate basis LIBOR  
Interest rate margin 1.45%  
Credit Agreement | LIBOR | Minimum    
Debt Instrument [Line Items]    
Interest rate margin 0.75%  
Credit Agreement | LIBOR | Maximum    
Debt Instrument [Line Items]    
Interest rate margin 1.90%  
Credit Agreement | Base Rate    
Debt Instrument [Line Items]    
Variable rate basis Base Rate  
Interest rate margin 0.45%  
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 0.90%  
Letters of credit    
Debt Instrument [Line Items]    
Commitment fee rate 0.225%  
Letter of credit fees 1.45%  
Required interest coverage ratio 3.50  
Letters of credit | Minimum    
Debt Instrument [Line Items]    
Commitment fee rate 0.075%  
Letter of credit fees 0.75%  
Letters of credit | Maximum    
Debt Instrument [Line Items]    
Commitment fee rate 0.375%  
Letter of credit fees 1.90%  
Required debt to capital ratio (less than 55%) 0.55