Debt (Details) (USD $) In Millions, unless otherwise specified								9 Months Ended							9 Months Ended
	Mar. 31, 2013 Credit Agreement	Mar. 31, 2013 Credit Agreement LIBOR	Mar. 31, 2013 Credit Agreement LIBOR Minimum	Mar. 31, 2013 Credit Agreement LIBOR Maximum	Mar. 31, 2013 Credit Agreement Base Rate	Mar. 31, 2013 Credit Agreement Base Rate Minimum	Mar. 31, 2013 Credit Agreement Base Rate Maximum	Mar. 31, 2013 Letters of credit	Mar. 31, 2013 Letters of credit Minimum	Mar. 31, 2013 Letters of credit Maximum	Mar. 31, 2013 Letters of credit LIBOR	Mar. 31, 2013 Letters of credit Base Rate	Mar. 31, 2013 4.45% Senior Notes due 2023	Feb. 26, 2013 4.45% Senior Notes due 2023	Mar. 31, 2013 Senior unsecured notes due May 2013
Secured and unsecured debt obligations
Face amount														$ 300
Interest rate (as a percent)													4.45%
Expected repayment of principal amount															100
Maximum borrowing capacity	350
Variable rate basis											LIBOR	Base Rate
Interest rate margin (as a percent)		1.20%	0.65%	1.95%	0.20%	0.00%	0.95%
Credit facility, fees rate (as a percent)								0.20%	0.10%	0.45%
Letter of credit fees (as a percent)								1.20%	0.65%	1.95%
Letters of credit issued	7.2
Credit Agreement available for future borrowings	$ 342.8
Required interest coverage ratio								3.5
Required debt to capital ratio										0.55