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STOCKHOLDERS' EQUITY - STOCK OPTIONS OUTSTANDING (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Performance-Based Stock Options
Options Outstanding
Number of Shares | shares	4,500,000
$1.10 - $1.72
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 1.10
Exercise price, high end of range (in dollars per share)	$ 1.72
Options Outstanding
Number of Shares | shares	10,290,050
Weighted Average Exercise Price Per Share (in dollars per share)	$ 1.61
Weighted Average Remaining Contractual Life (In years)	7 years 14 days
$1.73 - $2.45
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 1.73
Exercise price, high end of range (in dollars per share)	$ 2.45
Options Outstanding
Number of Shares | shares	7,144,384
Weighted Average Exercise Price Per Share (in dollars per share)	$ 2.27
Weighted Average Remaining Contractual Life (In years)	7 years 7 months 24 days
$2.54 - $5.01
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 2.54
Exercise price, high end of range (in dollars per share)	$ 5.01
Options Outstanding
Number of Shares | shares	8,055,105
Weighted Average Exercise Price Per Share (in dollars per share)	$ 3.95
Weighted Average Remaining Contractual Life (In years)	6 years 21 days
$5.09 - $7.31
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 5.09
Exercise price, high end of range (in dollars per share)	$ 7.31
Options Outstanding
Number of Shares | shares	1,796,413
Weighted Average Exercise Price Per Share (in dollars per share)	$ 5.33
Weighted Average Remaining Contractual Life (In years)	4 years 10 days
$1.10 - $7.31
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 1.10
Exercise price, high end of range (in dollars per share)	$ 7.31
Options Outstanding
Number of Shares | shares	27,285,952
Weighted Average Exercise Price Per Share (in dollars per share)	$ 2.72
Weighted Average Remaining Contractual Life (In years)	6 years 8 months 15 days

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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