Revolving Credit Agreement (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Mar. 31, 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 350
Revolving Credit Agreement, expiration date	June 21, 2016
Interest on the borrowings, variable rates	0.20%
Letters of credit issued	5.9
Revolving credit available for future borrowings	$ 344.1
Interest coverage ratio	3.5
Debt to capital ratio	55.00%
Maximum [Member]
Line of Credit Facility [Line Items]
Credit facility, fees rate	0.45%
Minimum [Member]
Line of Credit Facility [Line Items]
Credit facility, fees rate	0.10%
Base Rate [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	0.00%
Base Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	0.95%
Base Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	0.00%
LIBOR [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	1.20%
LIBOR [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	1.95%
LIBOR [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	0.65%
Letters Of Credit [Member]
Line of Credit Facility [Line Items]
Interest on the borrowings, variable rates	1.20%
Letters Of Credit [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Credit facility, fees rate	1.95%
Letters Of Credit [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Credit facility, fees rate	0.65%