Compensation Plan for Board Members - Additional Information (Detail) - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Board of Directors [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Issuance of common stock to board members in lieu of cash payments for quarterly board fees (shares)	146,371	90,306

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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Balance Type:	na
Period Type:	duration