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STOCK BASED COMPENSATION (Details) (USD $)
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1 Months Ended | 12 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Sep. 30, 2013
item
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Dec. 31, 2013
item
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2013
Research and development
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Dec. 31, 2012
Research and development
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Dec. 31, 2011
Research and development
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Dec. 31, 2013
General and administrative
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Dec. 31, 2012
General and administrative
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Dec. 31, 2011
General and administrative
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Sep. 30, 2013
Restructuring charges
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Dec. 31, 2013
Restructuring charges
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| Stock-based compensation expense related to stock-based awards | ||||||||||||
| Total stock-based compensation expense | $ 7,166,000 | $ 12,617,000 | $ 13,168,000 | $ 3,930,000 | $ 7,050,000 | $ 9,277,000 | $ 2,997,000 | $ 5,567,000 | $ 3,891,000 | $ 239,000 | $ 239,000 | |
| Reduction in workforce (as a percent) | 18.00% | |||||||||||
| Number of positions eliminated | 30 | |||||||||||
| Period for exercise of vested options for terminated employees, excluding employees covered under restructuring | 90 days | |||||||||||
| Number of terminated employees whose vesting period for unvested stock options was accelerated | 1 | |||||||||||