STOCKHOLDERS' EQUITY, STOCK-BASED COMPENSATION AND NET LOSS PER SHARE - Summary of Activity Under Equity Incentive Plans Related to Equity-Classified Stock Option Grants (Details)
$ / shares in Units, $ in Thousands |
12 Months Ended |
|
Dec. 31, 2019
USD ($)
$ / shares
shares
|
|---|
| Stock Options |
|
| Shares |
|
| Outstanding at beginning of period (in shares) | shares |
10,874,849
|
| Granted (in shares) | shares |
805,250
|
| Exercised (in shares) | shares |
(2,250)
|
| Forfeited, cancelled or expired (in shares) | shares |
(1,318,770)
|
| Outstanding at end of period (in shares) | shares |
10,359,079
|
| Options exercisable at end of period (in shares) | shares |
9,748,892
|
| Weighted-Average Exercise Price (in dollars per share) |
|
| Outstanding at beginning of period (in dollars per share) | $ / shares |
$ 4.36
|
| Granted (in dollars per share) | $ / shares |
0.73
|
| Exercised (in dollars per share) | $ / shares |
1.99
|
| Forfeited, cancelled or expired (in dollars per share) | $ / shares |
3.37
|
| Outstanding at end of period (in dollars per share) | $ / shares |
4.20
|
| Options exercisable at end of period (in dollars per share) | $ / shares |
$ 4.42
|
| Weighted-Average Remaining Contractual Term (in years) |
|
| Outstanding at end of period |
6 years 9 months 18 days
|
| Options exercisable at end of period |
6 years 7 months 6 days
|
| Aggregate Intrinsic Value (in thousands) |
|
| Outstanding at end of period | $ |
$ 0
|
| Options exercisable at end of period | $ |
$ 0
|
| China |
|
| Shares |
|
| Outstanding at beginning of period (in shares) | shares |
1,464,750
|
| Granted (in shares) | shares |
152,000
|
| Forfeited, cancelled or expired (in shares) | shares |
(518,000)
|
| Outstanding at end of period (in shares) | shares |
1,098,750
|
| Options exercisable at end of period (in shares) | shares |
911,500
|
| Weighted-Average Exercise Price (in dollars per share) |
|
| Outstanding at beginning of period (in dollars per share) | $ / shares |
$ 5.60
|
| Granted (in dollars per share) | $ / shares |
1.56
|
| Forfeited, cancelled or expired (in dollars per share) | $ / shares |
5.11
|
| Outstanding at end of period (in dollars per share) | $ / shares |
5.21
|
| Options exercisable at end of period (in dollars per share) | $ / shares |
$ 5.20
|
| Weighted-Average Remaining Contractual Term (in years) |
|
| Outstanding at end of period |
6 years 4 months 24 days
|
| Options exercisable at end of period |
6 years
|
| Aggregate Intrinsic Value (in thousands) |
|
| Outstanding at end of period | $ |
$ 0
|
| Options exercisable at end of period | $ |
$ 0
|