Stock-Based Compensation

3 Months Ended

Mar. 31, 2019

NOTE 9. STOCK-BASED COMPENSATION

The following table presents stock-based compensation expense recognized for stock options, restricted stock units, or RSUs, performance-based restricted stock units, or PRSUs, and the Company’s employee stock purchase program, or ESPP, in the Company’s statements of operations (in thousands):


	Three Months Ended
	March 31,
	2019		2018

Research and development	$	760	$	907
General and administrative		1,162		1,518
Total	$	1,922	$	2,425

In July 2018, the Company granted 903,374 PRSUs to its employees that vest upon the achievement of certain performance conditions, subject to the employees’ continued service relationship with the Company through the achievement date. At March 31, 2019, 878,289 of these PRSUs were outstanding. Based on the evaluation of the performance conditions at March 31, 2019, the Company has not recorded stock-based compensation expense for the three months ended March 31, 2019 related to these PRSUs. The Company will continue to evaluate the performance conditions for these PRSUs at each reporting period and will record compensation expense related to the PRSUs accordingly.

During the three months ended March 31, 2019, the Company had total unrecognized stock-based compensation expense, net of estimated forfeitures, of the following:



	Three Months Ended
	March 31, 2019
	Unrecognized Compensation Expense		Average Vesting Period
	($ million)		(Years)
Stock options grants	$	11.7	3.2
RSU grants		0.1	1.6
PRSU grants		—	—
ESPP		0.1	0.4

Option Exercises

For each of the three months ended March 31, 2019 and 2018, options were exercised to purchase 770 and zero shares, respectively, of the Company's common stock, with insignificant net proceeds to the Company in the three months ended March 31, 2019.

Restricted Stock Units

For each of the three months ended March 31, 2019 and 2018, the Company issued zero shares of its common stock upon vesting of RSUs or PRSUs to its employees.

Employee Stock Purchase Plan

In February 2019, the Company sold 83,046 shares of its common stock under the ESPP. The shares were purchased by employees at a purchase price of $2.39 per share with proceeds to the Company of approximately $0.2 million. In February 2018, the Company sold 68,589 shares of its common stock under the ESPP. The shares were purchased by employees at a purchase price of $4.38 per share with proceeds to the Company of approximately $0.3 million.