Leases - Summary of lease cost (Details) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Leases [Abstract]
Operating lease cost	$ 3.8	$ 10.8
Short-term lease cost	0.9	2.7
Variable lease cost	0.1	0.3
Total lease cost	4.8	13.8
Operating cash flow payments from operating leases	3.9	10.5
Non-cash ROU assets obtained in exchange for lease obligations	$ 5.2	$ 18.7
Weighted-average remaining lease term - operating leases	8 years 2 months 12 days	8 years 2 months 12 days
Weighted-average discount rate - operating leases	3.90%	3.90%