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Post-Retirement Benefits - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Compensation And Retirement Disclosure [Abstract]    
Contributions to the Compensation Plan by the employer $ 0.9 $ 0.9
Contributions to the Compensation Plan by the employer in remainder of fiscal year 2018 $ 2.8