Leases - Summary of lease cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2020
Leases [Abstract]
Operating lease cost	$ 3.0	$ 3.8	$ 9.8	$ 10.8
Short-term lease cost	0.7	0.9	2.3	2.7
Variable lease cost	0.0	0.1	0.2	0.3
Sublease income	(0.3)	0.0	(0.5)	0.0
Total lease cost	3.4	4.8	11.8	13.8
Operating cash flow payments from operating leases	3.1	3.9	10.2	10.5
Non-cash ROU assets obtained in exchange for lease obligations	$ 0.0	$ 5.2	$ 1.4	$ 18.7
Weighted-average remaining lease term - operating leases	8 years 4 months 24 days		8 years 4 months 24 days		8 years 1 month 6 days
Weighted-average discount rate - operating leases	4.00%		4.00%		3.90%