Fair Value Measurements - Schedule of carrying amounts and estimated fair values of financial instruments not recorded at fair value in the financial statements (Details) - Level 2 - USD ($) $ in Millions	Sep. 30, 2018	Jun. 30, 2018
Carrying Value
Carrying amounts and estimated fair values of financial instruments not recorded at fair value
Long-term debt	$ 545.5	$ 545.7
Company-owned life insurance	17.0	16.4
Fair Value
Carrying amounts and estimated fair values of financial instruments not recorded at fair value
Long-term debt	550.8	558.3
Company-owned life insurance	$ 17.0	$ 16.4