Debt - Schedule of long-term debt outstanding (Details) - USD ($)	Mar. 31, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Total	$ 552,400,000	$ 550,600,000
Less: amounts due within one year	0	0
Long-term debt, net of current portion	$ 552,400,000	$ 550,600,000
Senior unsecured notes, 5.20% due July 2021
Debt Instrument [Line Items]
Interest rate	5.20%	5.20%
Face amount	$ 250,000,000.0	$ 250,000,000.0
Total	$ 252,800,000	$ 251,200,000
4.45% Senior Unsecured Notes due 2023
Debt Instrument [Line Items]
Interest rate	4.45%	4.45%
Face amount	$ 300,000,000.0	$ 300,000,000.0
Total	$ 299,600,000	$ 299,400,000