Share-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation awards	$ 900,000	$ 500,000	$ 2,300,000	$ 1,200,000
Number of stock option granted	0	0	0	128,000
Cash received from employees and non-employee directors stock option exercised			$ 82,000	$ 1,100,000
Intrinsic value of option exercised			$ 89,000	$ 1,900,000
Number of options exercised			16,000	287,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock awards granted	33,000	0	963,000	405,000
Weighted-average fair value of restricted stock unit granted			$ 5.21	$ 9.87

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of share options (or share units) granted during the period.

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Number of share options (or share units) exercised during the current period.

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