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Fair Value - Additional Information (Detail) - USD ($)
$ in Millions
Sep. 30, 2019
Jun. 30, 2019
Level 1 [Member] | Money Market Funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Available-for-sale securities, debt securities $ 331.0 $ 313.7