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SUBSEQUENT EVENTS (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Oct. 31, 2019 | Apr. 30, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Oct. 01, 2019
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |
Operating lease, right-of-use asset |  |  | $ 349,000 |  |  |  |  | $ 349,000 |  |
Issuance of common stock in connection with at market offering, net of issuance costs |  |  | $ 8,959,000 | $ 101,000 | $ 2,158,000 | $ 82,306,000 | $ 1,553,000 |  |  |
2018 Sales Agreement |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |
Issuance of common stock in connection with at market offering, net of issuance costs (in shares) |  |  | 6,197,956 |  | 636,053 |  |  | 6,306,342 | 10,083,079 |
Issuance of common stock in connection with at market offering, net of issuance costs |  |  | $ 8,959,000 |  | $ 2,158,000 |  |  | $ 9,060,000 | $ 38,366,000 |
New Jersey Office Space Lease |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |
Operating lease, initial term |  | 11 years |  |  |  |  |  |  |  |
Operating lease term, option to extend additional period |  | 5 years |  |  |  |  |  |  |  |
Operating lease initial term, aggregate minimum future lease payments |  | $ 3,696,000 |  |  |  |  |  |  |  |
Operating lease, rent abatement period |  | 7 months |  |  |  |  |  |  |  |
Subsequent Event | 2018 Sales Agreement |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |
Issuance of common stock in connection with at market offering, net of issuance costs (in shares) | 6,908,525 |  |  |  |  |  |  |  |  |
Issuance of common stock in connection with at market offering, net of issuance costs | $ 10,232,000 |  |  |  |  |  |  |  |  |
Subsequent Event | Foster City | Office Space |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |
Operating lease, initial term | 87 months |  |  |  |  |  |  |  |  |
Operating lease term, option to extend additional period | 5 years |  |  |  |  |  |  |  |  |
Operating lease initial term, aggregate minimum future lease payments | $ 4,400,000 |  |  |  |  |  |  |  |  |
Operating lease, rent abatement period | 3 months |  |  |  |  |  |  |  |  |
Subsequent Event | New Jersey Office Space Lease |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |
Operating lease, initial term |  |  |  |  |  |  |  |  |  | 11 years
Operating lease, right-of-use asset |  |  |  |  |  |  |  |  |  | $ 2,400,000
Operating lease liability |  |  |  |  |  |  |  |  |  | $ 2,400,000
Operating lease incremental borrowing rate |  |  |  |  |  |  |  |  |  | 8.00%
Operating lease initial term, aggregate minimum future lease payments |  |  |  |  |  |  |  |  |  | $ 3,696,000

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