Fair Value of Financial Instruments - Additional Information (Detail)	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Available-for-sale Securities [Member] \| Certificates of Deposit [Member] \| Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments maturity period	1 year	1 year

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