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Post-Retirement Benefits - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Compensation And Retirement Disclosure [Abstract]        
Contributions to the Compensation Plan by the employer $ 0.9 $ 0.8 $ 2.8 $ 2.6
Contributions to the Compensation Plan by the employer in remainder of fiscal year 2018 $ 0.9   $ 0.9