Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Granted			625
Weighted-average grant date fair value per share of stock options			$ 6.19	$ 3.80
Aggregate intrinsic value of options exercised	$ 0	$ 900,000	$ 0	$ 2,300,000
Unrecognized stock-based compensation expense related to nonvested stock awards	$ 6,400,000		$ 6,400,000
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized			2 years 3 months 21 days
Stock Incentive Plan 2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for grant (in shares)	600		600
Number of Options, Granted			600	1,900
Stock Incentive Plan 2011 [Member] \| Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period			3 years
Stock Incentive Plan 2011 [Member] \| Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period			1 year