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STOCKHOLDERS' EQUITY - AT MARKET ISSUANCE SALES AGREEMENT (Details) - USD ($) |  | 3 Months Ended
--- | --- | ---
Aug. 28, 2015 | Mar. 31, 2018
At Market Issuance Sales Agreements [Line Items] |  |
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs |  | $ 1,553,000
2015 Sales Agreement |  |
At Market Issuance Sales Agreements [Line Items] |  |
Aggregate offering price of common stock | $ 50,000,000 |
Maximum commission rate (as a percent) | 3.00% |
Issuance of common stock in connection with at market offering (in shares) |  | 776,788
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs |  | $ 1,553,000

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