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Retirement Plans - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Dec. 31, 2018
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2016
Retirement Benefits [Abstract]        
Maximum percentage of eligible compensation matched by employer 5.00%      
Employer contributions to retirement plans $ 216,000 $ 220,000 $ 193,000 $ 209,000