Debt - Narrative (Details)	3 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Debt Instrument [Line Items]
Interest costs	$ 7,200,000	$ 7,700,000
Interest costs, capitalized	600,000	$ 700,000
Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	500,000,000
Letters of credit issued	7,100,000
Credit Agreement available for future borrowings	$ 492,900,000
Credit Agreement | LIBOR
Debt Instrument [Line Items]
Variable rate basis	LIBOR
Interest rate margin (as a percent)	1.25%
Credit Agreement | Base Rate
Debt Instrument [Line Items]
Variable rate basis	Base Rate
Interest rate margin (as a percent)	0.25%
Letters of credit
Debt Instrument [Line Items]
Commitment fee rate (as a percent)	0.15%
Letter of credit fees (as a percent)	1.25%
Required interest coverage ratio	3.50
Minimum | Credit Agreement | LIBOR
Debt Instrument [Line Items]
Interest rate margin (as a percent)	0.75%
Minimum | Credit Agreement | Base Rate
Debt Instrument [Line Items]
Interest rate margin (as a percent)	0.00%
Minimum | Letters of credit
Debt Instrument [Line Items]
Commitment fee rate (as a percent)	0.075%
Letter of credit fees (as a percent)	0.75%
Maximum | Credit Agreement | LIBOR
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.90%
Maximum | Credit Agreement | Base Rate
Debt Instrument [Line Items]
Interest rate margin (as a percent)	0.90%
Maximum | Letters of credit
Debt Instrument [Line Items]
Commitment fee rate (as a percent)	0.375%
Letter of credit fees (as a percent)	1.90%
Required debt to capital ratio (less than 55%)	0.55