STOCK-BASED COMPENSATION (Tables)
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12 Months Ended |
Dec. 31, 2017 |
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| STOCK-BASED COMPENSATION |
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| Schedule of stock-based compensation expense related to all of the entity's share-based awards |
Total stock‑based compensation expense related to all of our stock‑based awards was as follows (in thousands):
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Year Ended December 31,
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2017
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2016
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2015
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General and administrative
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$
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4,490
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$
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4,230
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$
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3,303
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Research and development
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1,497
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3,103
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4,100
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Restructuring charges
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—
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499
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—
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Total stock-based compensation expense
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$
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5,987
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$
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7,832
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$
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7,403
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| Summary of weighted-average assumptions relating to options granted pursuant to equity incentive plans |
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Year Ended
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December 31,
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2017
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2016
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2015
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Risk-free interest rate
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2.2
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%
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1.8
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%
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1.8
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%
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Expected term (in years)
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6.6
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6.2
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6.5
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Dividend yield
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0.0
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%
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0.0
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%
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0.0
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%
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Expected volatility
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63.5
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%
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61.1
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%
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65.0
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%
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| Schedule of option activity under equity incentive plans |
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Weighted-
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Average
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Remaining
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Shares Available
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Number of Shares
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Weighted-Average
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Contractual Term
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Aggregate
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For Grant
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Underlying Options
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Exercise Price
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(in years)
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Intrinsic Value
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Outstanding at January 1, 2017
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6,548,696
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20,257,233
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$
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6.24
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Authorized for grant
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6,460,000
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—
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Granted
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(4,048,675)
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4,048,675
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$
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2.42
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Exercised
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—
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(1,161,093)
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$
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2.30
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Cancelled
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2,736,675
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(2,736,675)
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$
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8.18
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Outstanding at December 31, 2017
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11,696,696
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20,408,140
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$
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5.45
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5.23
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$
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13,736,285
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Vested and expected to vest at December 31, 2017
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20,408,140
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$
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5.45
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Exercisable at December 31, 2017
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15,742,515
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$
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6.25
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4.16
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$
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8,298,096
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| Schedule of stock options by exercise price |
Details of our stock options by exercise price are as follows as of December 31, 2017:
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Options Outstanding
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Options Exercisable
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Number of
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Weighted-Average
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Outstanding
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Remaining
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Weighted-Average
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Number of
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Weighted-Average
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Exercise Price
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Options
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Contractual Life (in years)
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Exercise Price
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Options
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Exercise Price
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$1.68 - $2.14
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4,351,726
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7.25
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$
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2.12
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2,389,173
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$
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2.14
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$2.27 - $2.74
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3,682,677
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7.83
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2.60
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2,439,679
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2.68
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$2.89 - $3.67
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3,449,971
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5.57
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3.49
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2,859,448
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3.46
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$3.79 - $6.51
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3,831,410
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4.63
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5.62
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2,961,860
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6.13
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$6.55 - $9.62
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4,068,512
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2.29
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7.90
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4,068,512
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7.90
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$9.80 - $26.45
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1,023,844
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0.13
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26.02
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1,023,844
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26.02
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$1.68 - $26.45
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20,408,140
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5.23
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5.45
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15,742,516
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6.25
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| Summary of weighted-average assumptions used to calculate fair value of purchase rights granted under Employee Stock Purchase Plan |
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Year Ended
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December 31,
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2017
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2016
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2015
|
|
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Risk-free interest rate
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0.5
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%
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0.5
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%
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0.6
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%
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Expected term (in years)
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1.5
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1.5
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1.5
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Dividend yield
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0.0
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%
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0.0
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%
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0.0
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%
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Expected volatility
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63.1
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%
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62.9
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%
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61.2
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%
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