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SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 22, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Subsequent Event [Line Items] |  |  |  |
Stock options granted in period (in shares) |  | 442,956 | 738,893 | 449,537
Grants in period, weighted average exercise price (in dollars per share) |  | $ 1.75 | $ 2.34 | $ 2.13
Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Grants in period, weighted average exercise price (in dollars per share) | $ 2.92 |  |  |
Employee Stock Option |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Stock options granted in period (in shares) |  | 420,000 | 740,000 | 450,000
Award vesting period |  | 2 years |  |
Employee Stock Option | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Stock options granted in period (in shares) | 350,000 |  |  |
Award vesting period | 5 years |  |  |
Employee Stock Option | Share-based Compensation Award, Tranche One | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Award vesting rights, percentage | 50.00% |  |  |
Employee Stock Option | Share-based Compensation Award, Tranche Two | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Award vesting rights, percentage | 25.00% |  |  |
Employee Stock Option | Share-based Compensation Award, Tranche Three | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Award vesting rights, percentage | 25.00% |  |  |
Stock Appreciation Rights (SARs) | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Stock options granted in period (in shares) | 2,200,000 |  |  |
Award vesting period | 5 years |  |  |
Grants in period, weighted average exercise price (in dollars per share) | $ 2.92 |  |  |
Stock Appreciation Rights (SARs) | Share-based Compensation Award, Tranche One | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Grants in period, weighted average exercise price (in dollars per share) | $ 5.00 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Period Of Exercise Price | 90 days |  |  |
Stock Appreciation Rights (SARs) | Share-based Compensation Award, Tranche Two | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Grants in period, weighted average exercise price (in dollars per share) | $ 7.00 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Period Of Exercise Price | 90 days |  |  |
Stock Appreciation Rights (SARs) | Share-based Compensation Award, Tranche Three | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Grants in period, weighted average exercise price (in dollars per share) | $ 10.00 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Period Of Exercise Price | 90 days |  |  |
Restricted Stock Units (RSUs) |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Shares granted in share-based compensation awards (in shares) |  | 1,190,000 | 1,390,000 | 1,210,000
Award vesting period |  | 3 years |  |
Restricted Stock Units (RSUs) | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Shares granted in share-based compensation awards (in shares) | 720,000 |  |  |
Restricted Stock Units (RSUs) | Share-based Compensation Award, Tranche Four | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Award vesting rights, percentage | 50.00% |  |  |
Restricted Stock Units (RSUs) | Share-based Compensation Award, Tranche Five | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Award vesting rights, percentage | 25.00% |  |  |
Restricted Stock Units (RSUs) | Share-based Compensation Award, Tranche Six | Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Award vesting rights, percentage | 25.00% |  |  |
At The Market Sale Of Stock |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Sale of stock, number of shares issued (in shares) |  | 14,283,254 |  | 200,225
Sale of stock consideration received |  | $ 32,190 | $ 14,550 | $ 540

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