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Stock-Based Compensation (Tables)
3 Months Ended
Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Fair Value of Employee Stock Option Grants With Both Time-Based and Performance-Based Vesting Provisions

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants with both time-based and performance-based vesting provisions were as follows:

 

 

 

Three Months Ended March 31, 2018

 

 

Three Months Ended March 31, 2017

 

 

 

Time-Based

Vesting Provisions

 

 

Time-Based

Vesting Provisions

 

 

Performance-Based

Vesting Provisions

 

Risk-free interest rate

 

2.62% - 2.73%

 

 

 

2.17

%

 

1.98% - 2.17%

 

Expected volatility

 

86.2% - 86.7%

 

 

 

76.0

%

 

75.2% - 76.3%

 

Weighted-average volatility

 

 

86.6

%

 

 

76.0

%

 

 

75.9

%

Dividend yield

 

 

0

%

 

 

0

%

 

 

0

%

Weighted-average expected term

   (in years)

 

 

6.1

 

 

 

6.1

 

 

 

6.3

 

Weighted-average grant date fair

   value per share

 

$

8.29

 

 

$

6.79

 

 

$

6.73

 

 

Summary of Total Non-Cash Stock-Based Compensation Expense for All Stock Awards and Purchase Rights, Net of Forfeitures Recognized

Total non-cash stock-based compensation expense for all stock awards and purchase rights, net of forfeitures recognized as they occur, that was recognized in the statements of operations is as follows (in thousands):

 

 

 

Three Months Ended

March 31,

 

 

 

2018

 

 

2017

 

Research and development

 

$

747

 

 

$

142

 

General and administrative

 

 

774

 

 

 

387

 

Total

 

$

1,521

 

 

$

529