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STOCKHOLDERS' EQUITY-Common stock and warrants (Details) - USD ($) $ / shares in Units, $ in Millions | Feb. 09, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Sep. 09, 2016
--- | --- | --- | --- | ---
Stockholders' equity |  |  |  |
Shares issued | 9,200,000 |  |  |
Authorized shares of common stock, after amendment of certificate of incorporation |  | 1,000,000,000 | 1,000,000,000 |
Common stock, par value (in dollars per share) | $ 0.0001 | $ 0.0001 | $ 0.0001 |
Number of warrants issued |  |  |  | 4,700,000
Share price (in dollars per share) | $ 6.90 |  |  |
Net proceeds issuance of common stock | $ 60.4 |  |  |
Warrants Issued to Former Holders of Unsecured and Convertible Notes |  |  |  |
Stockholders' equity |  |  |  |
Number of warrants issued |  |  |  | 4,700,000
Exercise price (in dollars per share) |  |  |  | $ 14.04

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