STOCK-BASED COMPENSATION - Schedule of Stock Based Compensation Expense Recognized (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Stock-based compensation
Total	$ 2,702	$ 2,234
Cost of sales
Stock-based compensation
Total	0	14
Research and development expense
Stock-based compensation
Total	273	53
Selling, general and administrative expense
Stock-based compensation
Total	2,429	1,909
Restructuring
Stock-based compensation
Total	0	$ 258
Stock Options
Stock-based compensation
Total unrecognized compensation expense	$ 2,700
Average vesting period for recognition of unrecognized compensation expense	1 year 11 months 1 day
Restricted Stock Units and Performance-based Restricted Stock Units
Stock-based compensation
Average vesting period for recognition of unrecognized compensation expense	2 years 3 months 26 days
Total unrecognized compensation expense	$ 22,900
Restricted Stock Units
Stock-based compensation
Award granted (in shares)	1.9
Granted (in dollars per share)	$ 4.38
Performance-based Restricted Stock Units
Stock-based compensation
Award granted (in shares)	0.6
Granted (in dollars per share)	$ 6.87

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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