Marketable Debt Securities - Additional Information (Detail) $ in Millions	Sep. 30, 2018 USD ($)
Prepaid Expenses and Other Current Assets
Marketable Securities [Line Items]
Receivable due for marketable securities	$ 29.7

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration