Share Based Payments - Summary of Stock Option Activity (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2017 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock options exercised on cashless basis	20,000
Number of common stock shares withheld	14,095

Stock issued during period shares stock options exercised on cashless basis.

No definition available.

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Period Type:	duration