STOCK-BASED COMPENSATION - SCHEDULE OF STOCK OPTIONS, MARKET CONDITION BASED STOCK OPTIONS AND EMPLOYEE STOCK PURCHASE PLAN VALUATION ASSUMPTIONS (Detail)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)		6 months	6 months	6 months
Volatility		46.00%	58.00%	48.00%
Interest rate		1.10%	1.90%	0.90%
Standard Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)	4 years 5 months 19 days	4 years 7 months 6 days	4 years 5 months 1 day	4 years 6 months
Volatility	55.00%	53.00%	55.00%	53.00%
Interest rate	2.70%	1.70%	2.50%	1.70%
Market Condition Based Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)			7 years	7 years
Volatility			55.00%	55.00%
Interest rate			2.00%	2.00%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own 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

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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