Post-Retirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Contributions to the Compensation Plan by the employer	$ 1.0	$ 0.9	$ 1.9	$ 1.8
Contributions to the Compensation Plan by the employer in remainder of fiscal year 2018	$ 1.8		$ 1.8