Debt - Schedule of Long-term Debt Outstanding (Details) - USD ($)	Jun. 30, 2016	Jun. 30, 2015
Revolving Credit Agreement
Long-term Debt	$ 611,300,000	$ 603,800,000
Long-term debt, net of current portion	611,300,000	603,800,000
Medium-term notes, Series B at 6.97% to 7.10% due from April 2018 to May 2018 (face value of $55.0 million at June 30, 2016 and 2015)
Revolving Credit Agreement
Face amount	55,000,000.0	55,000,000.0
Long-term Debt	$ 55,000,000	$ 55,000,000
Medium-term notes, Series B at 6.97% to 7.10% due from April 2018 to May 2018 (face value of $55.0 million at June 30, 2016 and 2015) | Minimum
Revolving Credit Agreement
Interest rate	6.97%	6.97%
Medium-term notes, Series B at 6.97% to 7.10% due from April 2018 to May 2018 (face value of $55.0 million at June 30, 2016 and 2015) | Maximum
Revolving Credit Agreement
Interest rate	7.10%	7.10%
Senior unsecured notes, 5.20% due July 2021 (face value of $250.0 million at June 30, 2016 and 2015)
Revolving Credit Agreement
Interest rate	5.20%	5.20%
Face amount	$ 250,000,000.0	$ 250,000,000.0
Long-term Debt	$ 257,800,000	$ 250,500,000
Senior unsecured notes, 4.45% due March 2023 (face value of $300.0 million at June 30, 2016 and 2015)
Revolving Credit Agreement
Interest rate	4.45%	4.45%
Face amount	$ 300,000,000.0	$ 300,000,000.0
Long-term Debt	$ 298,500,000	$ 298,300,000