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Revenue - Reconciliation of Deferred Revenue Balances (Detail) - USD ($)
$ in Millions
3 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Revenue From Contract With Customer [Abstract]    
Deferred revenue - beginning balance $ 2.6 $ 2.6
Revenue recognized (1.7) (5.9)
Prepayments 1.6 6.2
Deferred revenue - Ending Balance $ 2.5 $ 2.9