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Stock-Based Compensation
 6 Months Ended
Jun. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock-Based Compensation STOCK-BASED COMPENSATION
The following table shows total stock-based compensation expense included in the Condensed Consolidated Statements of Operations for the three and six months ended June 30, 2019 and 2018 (in thousands):

Three Months Ended
June 30,

Six Months Ended
June 30,

2019

2018

2019

2018
Research and development
$
2,763


$
2,120


$
5,061


$
3,879

General and administrative
2,104


1,394


4,329


2,685

Total stock-based compensation expense
$
4,867


$
3,514


$
9,390


$
6,564