Leases - Summary of lease cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2020
Leases [Abstract]
Operating lease cost	$ 3.2	$ 3.5	$ 6.8	$ 7.0
Short-term lease cost	0.7	0.8	1.6	1.6
Variable lease cost	0.1	0.1	0.2	0.2
Sublease income	(0.2)	0.0	(0.3)	0.0
Total lease cost	3.8	4.4	8.3	8.8
Operating cash flow payments from operating leases	3.3	3.4	6.9	6.7
Non-cash ROU assets obtained in exchange for lease obligations	$ 0.0	$ 11.4	$ 1.4	$ 12.3
Weighted-average remaining lease term - operating leases	8 years		8 years		8 years 1 month 6 days
Weighted-average discount rate - operating leases	3.90%		3.90%		3.90%