STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares
Options outstanding, beginning (shares)	8,170	8,632	8,509
Granted (shares)	2,440	1,289	1,311
Exercised (shares)	(375)	(1,079)	(886)
Canceled (shares)	(1,505)	(672)	(302)
Options outstanding, ending (shares)	8,730	8,170	8,632
Weighted- Average Exercise Price per Share
Options outstanding, beginning (usd per share)	$ 5.36	$ 4.75	$ 3.94
Granted (usd per share)	2.12	8.20	10.36
Exercised (usd per share)	0.39	1.40	4.33
Canceled (usd per share)	6.01	9.31	7.58
Options outstanding, ending (usd per share)	$ 4.55	$ 5.36	$ 4.75

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)-(4)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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