SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| EPS Numerator: | |||||||||||
| Net loss | $ (25,871) | $ (17,660) | $ (19,147) | $ (15,314) | $ (15,590) | $ (22,629) | $ (13,533) | $ (17,464) | $ (77,992) | $ (69,216) | $ (51,464) |
| EPS Denominator - Basic and Diluted: | |||||||||||
| Weighted average common shares outstanding | 144,252 | 124,628 | 122,500 | 113,598 | 98,981 | 95,454 | 92,495 | 90,555 | 126,324 | 94,387 | 88,434 |
| Net loss per common share: | |||||||||||
| Basic and diluted (in dollars per share) | $ (0.18) | $ (0.14) | $ (0.16) | $ (0.13) | $ (0.16) | $ (0.24) | $ (0.15) | $ (0.19) | $ (0.62) | $ (0.73) | $ (0.58) |
| Weighted Average | |||||||||||
| Net loss per common share: | |||||||||||
| Weighted average exercise price of options (in dollars per share) | $ 5.45 | 6.25 | $ 5.45 | 6.25 | 7.08 | ||||||
| Weighted average exercise price of warrant (in dollars per share) | $ 6.61 | $ 6.61 | $ 6.61 | ||||||||
| Employee stock option | |||||||||||
| Net loss per common share: | |||||||||||
| Antidilutive securities excluded from computation of earnings per share (in shares) | 20,408 | 20,257 | 19,106 | ||||||||
| Warrant to purchase common stock | |||||||||||
| Net loss per common share: | |||||||||||
| Antidilutive securities excluded from computation of earnings per share (in shares) | 32 | 200 | |||||||||