SHARE-BASED COMPENSATION - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Number of Shares under Option (in thousands)
Outstanding at beginning of period (in shares)	3,942
Granted (in shares)	3,986
Exercised (in shares)	(30)
Canceled or forfeited (in shares)	(1,448)
Outstanding at end of period (in shares)	6,450	3,942
Exercisable at end of period (in shares)	1,744
Weighted-average Exercise Price per Option
Outstanding at beginning of period (in dollars per share)	$ 2.12
Granted (in dollars per share)	1.02
Exercised (in dollars per share)	1.50
Canceled or forfeited (in dollars per share)	1.76
Outstanding at end of period (in dollars per share)	1.52	$ 2.12
Exercisable (in dollars per share)	$ 2.42
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average Remaining Contractual Life (in years), Outstanding	9 years 1 month 6 days	9 years 1 month 6 days
Weighted-average Remaining Contractual Life (in years), Exercisable	8 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding	$ 680	$ 57
Aggregate Intrinsic Value, Exercisable	$ 84

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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