SHARE-BASED COMPENSATION - 2015 Plan (Details) - 2015 Plan	6 Months Ended
Jun. 30, 2019 shares
Share-Based Compensation Awards
Shares reserved for issuance pursuant to the plan	4,500,000
Stock options \| Employees and nonemployees owning less than 10% of voting power
Share-Based Compensation Awards
Vesting period	4 years

Aggregate number of common shares reserved for future issuance.

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-Name Accounting Standards Codification
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
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