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Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2019
Share-based Payment Arrangement [Abstract]  
Schedule of stock option activity
The following table summarizes the activity related to stock option grants to employees and nonemployees for the years ended December 31, 2019:
 SharesWeighted
average
exercise price
per share		Weighted
average
remaining
contractual life
Outstanding at December 31, 20186,182,873  $10.60  6.67
Granted2,088,673  7.72  
Exercised(254,335) 4.09  
Expired—  —   
Forfeited(617,994) 12.96  
Outstanding at December 31, 20197,399,217  $9.81  6.37
Exercisable at December 31, 20194,287,676  $9.43  4.68
Vested and expected to vest at December 31, 20197,399,217  $9.81  6.37
Schedule of allocated stock-based compensation expense
The Company recorded stock-based compensation expense in the following expense categories of its accompanying consolidated statements of operations for the years ended December 31, 2019 and 2018:
Year Ended December 31,
 20192018
Cost of product sales$103  $9  
Research and development1,062  989  
Selling, general and administrative8,695  7,545  
Total stock-based compensation expense$9,860  $8,543  
Schedule of fair value options using Black-Scholes pricing model The Company calculated the fair value of each option grant and the shares issued under the 2017 Plan on the respective dates of grant using the following weighted average assumptions:
December 31, 2019
2010 A&R Stock Incentive Plan2017 Employee Stock Purchase Plan
Risk free interest rate2.47 %2.32 %
Expected term (in years)6.050.50
Expected volatility67.03 %73.34 %
Annual dividend yield0.00 %0.00 %