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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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Unrecognized cost of unvested options awarded to employees as compensation.

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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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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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Number of share instruments newly issued under a share-based compensation plan.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Share based compensation arrangement by share based payment award other than options expected to be released.

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Stock-Based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended
	Dec. 31, 2017	Nov. 30, 2017	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value of options granted, per share						$ 4.18	$ 3.13
Grant date fair value of options vested						$ 2,500,000	$ 1,900,000
Aggregate intrinsic value of option exercised						2,200,000	1,500,000
Unrecognized compensation cost				$ 14,800,000		$ 14,800,000
Weighted average period for recognition of compensation costs						3 years
Stock based compensation expenses				1,683,000	$ 1,013,000	$ 2,873,000	$ 1,782,000
Stock-based compensation expense capitalized				$ 0		$ 0
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Granted						0	0
Stock based compensation expenses						$ 0	$ 0
Restricted Stock Units (RSUs) \| Board of Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Granted		43,554	112,578
Grant date fair value of RSUs, per share	$ 3.58	$ 8.02	$ 3.58
RSUs Released	18,964
Restricted Stock Units (RSUs) \| Executive Officers
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Granted		12,468
Grant date fair value of RSUs, per share		$ 8.02
Restricted Stock Units (RSUs) \| Board of Directors (Departure 1)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs expected to released				34,502		34,502
RSUs expected to vest, fair value per share				$ 3.58		$ 3.58
Restricted Stock Units (RSUs) \| Board of Directors (Departure 2)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs expected to released				12,467		12,467
RSUs expected to vest, fair value per share				$ 8.02		$ 8.02