Leases - Summary of lease cost (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020
Leases [Abstract]
Operating lease cost	$ 3.6	$ 3.4
Short-term lease cost	0.8	0.8
Variable lease cost	0.2	0.1
Total lease cost	4.6	4.3
Operating cash flow payments from operating leases	3.5	3.3
Non-cash ROU assets obtained in exchange for lease obligations	$ 1.4	$ 0.9
Weighted-average remaining lease term - operating leases	8 years		8 years 1 month 6 days
Weighted-average discount rate - operating leases	3.90%		3.90%