Supplemental Financial Information - Noncash Investing and Financing Activities (Parenthetical) (Detail) - shares	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Restricted Stock [Member]
Condensed Financial Statements, Captions [Line Items]
Number of shares of common stock withheld	128,189	85,580

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
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Period Type:	duration