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Stock Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Stock Option Activity

The following table summarizes stock option activity, under our 2013 Plan and related information:

 

 

 

Shares

 

 

 

 

 

 

 

Subject to

 

 

Weighted-

 

 

 

Outstanding

 

 

Average Exercise

 

 

 

Stock Options

 

 

Price Per Share

 

Balance at December 31, 2014

 

 

4,249,168

 

 

$

14.77

 

Options granted

 

 

1,815,991

 

 

 

38.33

 

Options exercised

 

 

(1,095,486

)

 

 

10.14

 

Options canceled

 

 

(238,190

)

 

 

26.26

 

Balance at December 31, 2015

 

 

4,731,483

 

 

$

24.19

 

 
Additional Information Related to the Status of Stock Options

Additional information related to the status of stock options at December 31, 2015, is as follows (aggregate intrinsic value in thousands):

 

 

 

 

 

 

 

Weighted-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Average

 

 

Remaining

 

 

 

 

 

 

 

 

 

 

 

Exercise Price

 

 

Contractual

 

 

Aggregate

 

 

 

Shares

 

 

Per Share

 

 

Life

 

 

Intrinsic Value

 

Outstanding

 

 

4,731,483

 

 

$

24.19

 

 

 

7.3

 

 

$

128,996

 

Vested and expected to vest

 

 

4,543,051

 

 

$

23.73

 

 

 

7.2

 

 

$

125,964

 

Vested

 

 

2,341,265

 

 

$

14.92

 

 

 

5.6

 

 

$

85,533

 

 
Stock Options Outstanding and Vested and Exercisable

Additional information regarding our stock options outstanding and vested and exercisable as of December 31, 2015 is summarized below:

 

 

 

Stock Options Outstanding

 

 

Stock Options Vested

 

 

 

 

 

 

 

Weighted

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Average

 

 

Weighted

 

 

Number

 

 

Weighted

 

 

 

Number of

 

 

Remaining

 

 

Average

 

 

of

 

 

Average

 

 

 

Stock Options

 

 

Contractual

 

 

Exercise Price

 

 

Stock Options

 

 

Exercise Price

 

Exercise Prices

 

Outstanding

 

 

Life (Years)

 

 

per Share

 

 

Vested

 

 

Per Share

 

$3.30 - $5.10

 

 

495,133

 

 

 

2.4

 

 

$

4.55

 

 

 

495,133

 

 

$

4.55

 

$5.30 -  $9.00

 

 

767,038

 

 

 

4.9

 

 

 

8.18

 

 

 

743,033

 

 

 

8.21

 

$9.50 - $22.16

 

 

483,519

 

 

 

7.3

 

 

 

15.29

 

 

 

321,529

 

 

 

14.88

 

$22.60-$25.00

 

 

330,676

 

 

 

7.9

 

 

 

23.95

 

 

 

162,964

 

 

 

23.95

 

$25.08-$25.08

 

 

523,124

 

 

 

8.0

 

 

 

25.08

 

 

 

251,396

 

 

 

25.08

 

$25.14-$29.19

 

 

522,962

 

 

 

8.7

 

 

 

27.57

 

 

 

170,511

 

 

 

27.83

 

$29.72-$29.72

 

 

542,160

 

 

 

8.8

 

 

 

29.72

 

 

 

127,311

 

 

 

29.72

 

$35.69-$44.39

 

 

578,896

 

 

 

9.0

 

 

 

40.82

 

 

 

53,971

 

 

 

42.84

 

$44.63 - $51.45

 

 

479,225

 

 

 

9.5

 

 

 

47.71

 

 

 

14,506

 

 

 

47.21

 

$52.74 - $52.74

 

 

8,750

 

 

 

9.6

 

 

 

52.74

 

 

 

911

 

 

 

52.74

 

 

 

 

4,731,483

 

 

 

7.3

 

 

$

24.19

 

 

 

2,341,265

 

 

$

14.92

 

 
Summary of RSU Activity

The following table summarizes RSU activity, under our 2013 Plan and related information:

 

 

 

Shares

 

 

 

 

 

 

 

Subject to

 

 

Weighted-

 

 

 

Outstanding

 

 

Average grant date

 

 

 

RSU's

 

 

fair value per share

 

Balance at December 31, 2014

 

 

–

 

 

$

–

 

RSUs granted

 

 

187,200

 

 

 

30.74

 

RSUs canceled

 

 

(19,450

)

 

 

29.72

 

Balance at December 31, 2015

 

 

167,750

 

 

$

30.86

 

 
Summary of PSU Activity

The following table summarizes PSU activity, under our 2013 Plan and related information:

 

 

 

Shares

 

 

 

 

 

 

 

Subject to

 

 

Weighted-

 

 

 

Outstanding

 

 

Average grant date

 

 

 

PSU's

 

 

fair value per share

 

Balance at December 31, 2014

 

 

–

 

 

$

–

 

PSUs granted

 

 

40,496

 

 

 

49.99

 

M-PSUs granted

 

 

165,000

 

 

 

24.29

 

PSUs canceled

 

 

(235

)

 

 

49.44

 

Balance at December 31, 2015

 

 

205,261

 

 

$

29.33

 

 
Classification of Stock-Based Compensation Expense

Stock-based compensation expense, net of estimated forfeitures, is reflected in the consolidated statements of operations as follows (in thousands):

 

 

 

Year Ended December 31,

 

 

 

2015

 

 

2014

 

 

2013

 

Research and development

 

$

11,653

 

 

$

4,551

 

 

$

2,295

 

Selling, general and administrative

 

 

11,205

 

 

 

4,782

 

 

 

2,679

 

Total stock-based compensation

 

$

22,858

 

 

$

9,333

 

 

$

4,974

 

 
Summary of Weighted-Average Assumptions of Fair Value Awards

The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of these awards:

 

 

 

Year Ended December 31,

 

 

 

2015

 

 

2014

 

 

2013

 

Risk-free interest rate

 

 

 

 

 

 

 

 

 

 

 

 

Stock options

 

1.54%-1.93%

 

 

1.81%-1.89%

 

 

 

1.43%

 

ESPP

 

 

0.14%

 

 

 

0.08%

 

 

–

 

Expected term

 

 

 

 

 

 

 

 

 

 

 

 

Stock options

 

6.0 years

 

 

6.0 years

 

 

6.0 years

 

ESPP

 

0.5 years

 

 

0.5 years

 

 

–

 

Expected volatility

 

 

 

 

 

 

 

 

 

 

 

 

Stock options

 

64% - 66%

 

 

69% - 80%

 

 

 

79%

 

ESPP

 

 

62%

 

 

 

73%

 

 

–

 

Dividend yield

 

 

 

 

 

 

 

 

 

 

 

 

Stock options

 

–

 

 

–

 

 

–

 

ESPP

 

–

 

 

–

 

 

–

 

 
Assumptions used to Determine Weighted-Average Fair Value of M-Performance Stock Units

The weighted-average fair value of the M-PSUs was determined using the Monte Carlo simulation models incorporating the following assumptions:

 

 

 

Year Ended

December 31, 2015

 

 

 

PSUs

 

Number of M-PSUs granted

 

 

165,000

 

Weighted-average grant date stock price

 

$

31.95

 

Weighted-average risk-free interest rate

 

 

1.13

%

Weighted-average volatility

 

 

62

%

Dividend yield

 

–

 

Weighted- average fair value per share of M-PSUs granted ($50 Vesting Hurdle)

 

$

24.22

 

Weighted- average fair value per share of M-PSUs granted ($60 Vesting Hurdle)

 

$

24.34