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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

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- Definition

Discount rate from fair value on purchase date that participants pay for shares.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Number of options outstanding, including both vested and non-vested options.

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Number of non-vested options outstanding.

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No definition available.

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Number of options vested.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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Equity - Narrative (Detail) - USD ($) $ in Millions			3 Months Ended
Equity - Narrative (Detail) - USD ($) $ in Millions	May 25, 2017	May 24, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option outstanding (in shares)			7,978,026		6,342,526
Stock options, granted (in shares)			1,720,500
Unrecognized stock-based compensation cost			$ 7.9
Unrecognized share-based compensation expense, weighted-average recognition period (in years)			1 year 3 months 18 days
Shares purchased by employees under ESPP			36,922	24,363
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Change in discount rate	15.00%	5.00%
Stock compensation expense (gain)			$ 0.1	$ 0.0
Non Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, granted (in shares)			1,180,000
Stock option vested (in shares)			445,833
Stock option unvested (in shares)			734,167
Unrecognized stock-based compensation cost			$ 0.9