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Stock-based Compensation (Tables)
9 Months Ended
Sep. 30, 2019
Summary of stock-based compensation

Three months ended September 30, 

Nine months ended September 30, 

2019

2018

2019

2018

Research and development expenses

$

525

    

$

388

$

1,606

    

$

1,091

Selling, general and administrative expenses

 

3,612

 

3,538

 

10,956

 

9,089

Total stock-based compensation expense

$

4,137

$

3,926

$

12,562

$

10,180

Summary of restricted stock units activity

Weighted-Average

Shares

Grant Date Fair Value

Outstanding at December 31, 2018

514,603

$

20.67

Granted

634,708

15.48

Vested

(185,605)

21.44

Forfeited

(95,631)

18.19

Outstanding at September 30, 2019

868,075

$

16.98

Summary of stock option activity

 

 

 

Weighted-

 

 

Weighted-

 

Average

 

Average

 

Remaining

Aggregate

Exercise Price

 

Contractual

Intrinsic

    

Shares

    

per Share

    

Term (in years)

    

Value

Outstanding at December 31, 2018

 

3,585,856

$

16.20

 

8.0

$

11,170

Granted

 

1,045,658

15.08

Exercised

 

(52,182)

10.27

Cancelled

 

(438,703)

17.96

Outstanding at September 30, 2019

 

4,140,629

$

15.81

 

7.7

$

3,611

Exercisable at September 30, 2019

 

2,147,473

$

14.61

 

6.7

$

3,108

Schedule of fair value assumption using Black-Scholes option-pricing model

Nine months ended September 30, 

2019

2018

Risk-free interest rate

2.4

%  

2.6

%  

Volatility

63.2

%  

65.0

%  

Expected term (years)

6.06

6.11

Expected dividend yield

%  

%  

Performance share units  
Summary of stock option activity

Weighted-Average

Shares

Grant Date Fair Value

Outstanding at December 31, 2018

$

Granted

99,400

15.90

Outstanding at September 30, 2019

99,400

$

15.90