Leases - Summary of lease cost (Details) $ in Millions	3 Months Ended	6 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 3.5	$ 7.0
Short-term lease cost	0.8	1.6
Variable lease cost	0.1	0.2
Total lease cost	4.4	8.8
Operating cash flow payments from operating leases	3.4	6.7
Non-cash ROU assets obtained in exchange for lease obligations	$ 11.4	$ 12.3
Weighted-average remaining lease term - operating leases	7 years 10 months 24 days	7 years 10 months 24 days
Weighted-average discount rate - operating leases	3.70%	3.70%