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Share Based Payments - Summary of Stock Option Activity (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2018 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock options exercised on cashless basis	80,000
Number of common stock shares withheld	17,091

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Number of common stock shares withheld.

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

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