Stock-Based Compensation

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

NOTE 5. 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,
	2018		2017

Research and development	$	907	$	1,031
General and administrative		1,518		1,078
Total	$	2,425	$	2,109

In January 2017, the Company granted PRSU awards to certain employees which vest upon the achievement of specified performance conditions, subject to the employees’ continued service relationship with the Company. None vested during the three months ended March 31, 2018. However, the related compensation cost is recognized as an expense over the estimated vesting period when achievement of the milestone is considered probable. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted. The Company recognized $0.1 million of related expense during the three months ended March 31, 2018, respectively.

At March 31, 2018, the Company had $16.0 million, $1.9 million, $0.5 million and $0.1 million of total unrecognized compensation expense, net of estimated forfeitures, related to stock option grants, RSU grants, PRSUs and the ESPP, respectively, that will be recognized over an average vesting period of 3.0 years, 1.2 years, 1.2 years and 0.4 years, respectively.

Option Exercises

For the three months ended March 31, 2018 and 2017, employees exercised options to purchase zero and 19,301 shares, respectively, of the Company's common stock, with insignificant net proceeds in the three months ended March 31, 2017.

Restricted Stock Units

For the three months ended March 31, 2018 and 2017, the Company issued zero and 15,188 shares, respectively, of its common stock upon vesting of restricted stock units.

Employee Stock Purchase Plan

In February 2018, the Company sold 68,589 shares under the ESPP. The shares were purchased at a purchase price of $4.38 per share with proceeds to the Company of approximately $0.3 million. In February 2017, the Company sold 42,845 shares under the ESPP. The shares were purchased at a purchase price of $8.77 per share with proceeds to the Company of approximately $0.4 million.