STOCKHOLDERS' EQUITY AND SHARE-BASED COMPENSATION PLANS - Expense by Classification (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense recognized	$ 7,338	$ 13,824
Compensation cost not yet recognized	$ 7,400
Weighted-average period over which compensation cost is expected to be recognized	1 year 11 months 23 days
Aggregate fair value of options and restricted shares vesting	$ 8,900	13,900
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense recognized	4,017	7,479
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense recognized	$ 3,321	$ 6,345

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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