Debt (Details) (USD $) In Millions, unless otherwise specified				12 Months Ended			0 Months Ended		12 Months Ended			12 Months Ended			12 Months Ended
	Jun. 30, 2013 4.45% Senior Notes due 2023	Feb. 26, 2013 4.45% Senior Notes due 2023	Jun. 30, 2012 4.45% Senior Notes due 2023	Jun. 30, 2013 Senior unsecured notes due May 2013	Jun. 30, 2013 Senior unsecured notes, 5.200% due July 2021	Jun. 30, 2012 Senior unsecured notes, 5.200% due July 2021	Jun. 28, 2013 Credit Agreement	Jun. 30, 2013 Credit Agreement	Jun. 30, 2013 Credit Agreement LIBOR	Jun. 30, 2013 Credit Agreement LIBOR Minimum	Jun. 30, 2013 Credit Agreement LIBOR Maximum	Jun. 30, 2013 Credit Agreement Base Rate	Jun. 30, 2013 Credit Agreement Base Rate Minimum	Jun. 30, 2013 Credit Agreement Base Rate Maximum	Jun. 30, 2013 Letters of credit	Jun. 30, 2013 Letters of credit Minimum	Jun. 30, 2013 Letters of credit Maximum
Secured and unsecured debt obligations
Face amount	$ 300.0	$ 300.0	$ 0		$ 250.0	$ 250.0
Interest rate (as a percent)	4.45%	4.45%	4.45%		5.20%	5.20%
Expected repayment of principal amount				100
Maximum borrowing capacity							500
Maturity term of debt instrument							5 years
Debt issuance costs								0.8
Variable rate basis									LIBOR			Base Rate
Interest rate margin (as a percent)									1.25%	0.75%	1.90%	0.25%	0.00%	0.90%
Commitment fee rate (as a percent)															0.15%	0.075%	0.375%
Letter of credit fees (as a percent)															1.25%	0.75%	1.90%
Letters of credit issued								7.2
Credit Agreement available for future borrowings								$ 492.8
Required interest coverage ratio															3.5
Required debt to capital ratio																	0.55