Stock-Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Stock Option Activity

A summary of the Company’s stock option activity under the 2013 Plan is as follows:

 

 

 

Number of

Shares

 

 

Weighted-

Average

Exercise

Price

 

Balances at December 31, 2017

 

 

4,196,203

 

 

 

3.06

 

Granted

 

 

493,776

 

 

 

5.79

 

Exercised

 

 

(400,587

)

 

 

3.10

 

Canceled

 

 

(25,423

)

 

 

3.39

 

Balances at March 31, 2018

 

 

4,263,969

 

 

 

3.37

 

 
Summary of Restricted Stock Activity

A summary of the Company’s restricted stock activity for the three months ended March 31, 2018:

 

 

 

Shares

 

 

Weighted

Average

Grant Date

Fair Value

 

Unvested at December 31, 2017

 

 

478,971

 

 

$

4.57

 

Granted

 

 

—

 

 

$

4.57

 

Vested

 

 

(119,742

)

 

$

4.57

 

Unvested at March 31, 2018

 

 

359,229

 

 

$

4.57

 

 
Summary of Stock-based Compensation Expense

The following table sets forth the total stock-based compensation expense for all options granted to employees and nonemployees, including shares sold through the issuance of non-recourse promissory notes which are considered to be options for accounting purposes, included in the Company’s statement of operations:

 

 

 

Three Months Ended

March 31,

 

 

 

2018

 

 

2017

 

 

 

(in thousands)

 

Research and development

 

$

974

 

 

$

170

 

General and administrative

 

 

396

 

 

 

243

 

Total

 

$

1,370

 

 

$

413