Share-Based Compensation

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Pursuant to the evergreen provisions of the Company's 2013 stock incentive plan (the "2013 Plan"), annual increases have resulted in the addition of an aggregate of approximately 10,539,000 additional shares to the 2013 Plan, including for 2020, an increase of approximately 1,985,000 shares, or approximately 4% of the total number of shares of the Company's common stock outstanding as of January 1, 2020. As of March 31, 2020, the Company had approximately 2,908,000 shares available for grant under the 2013 Plan.

In October 2019, the Company's board of directors adopted its 2019 Inducement Stock Incentive Plan (the “2019 Inducement Plan”) to reserve initially 1,000,000 shares of its common stock to be used exclusively for grants of awards to individuals who were not previously employees or directors of the Company as a material inducement to such individuals’ entry into employment with the Company within Rule 5635(c)(4) of the Nasdaq Listing Rules. The terms and conditions of the 2019 Inducement Plan are substantially similar to those of the 2013 Plan. In March 2020, the Company's board of directors amended the 2019 Inducement Plan to reserve an additional 1,000,000 shares of its common stock for issuance under the plan. As of March 31, 2020, the Company had approximately 1,622,000 shares available for grant under the 2019 Inducement Plan.

Share-based compensation expense, net of estimated forfeitures, includes expenses related to stock options and RSUs granted to employees, non-employee directors and consultants, as well as options granted to employees to purchase shares under the ESPP. Stock-based compensation by award type was as follows:



	Three Months Ended March 31,
	2020		2019
Stock options	$	1,374	$	1,622
Restricted stock units	936		821
Employee stock purchase plan	14		27
Total	$	2,324	$	2,470

The Company allocated stock-based compensation expense in the Company’s Consolidated Statements of Operations and Comprehensive Loss as follows:



	Three Months Ended March 31,
	2020		2019
Research and development	$	1,153	$	1,170
General and administrative	1,171		1,300
Total	$	2,324	$	2,470

Stock Options

A summary of the stock option activity, weighted average exercise prices, options outstanding, exercisable and expected to vest as of March 31, 2020 is as follows (in thousands except weighted average exercise price):



	Number of Shares Underlying Options		Weighted Average Exercise Price
Outstanding, December 31, 2019	6,780		$	10.89
Granted	105		$	6.58
Exercised	(49	)	$	2.78
Forfeited	(201	)	$	17.36
Outstanding, March 31, 2020	6,635		$	10.69
Vested and exercisable, March 31, 2020	3,482		$	17.07
Vested and expected to vest, March 31, 2020	6,383		$	10.97

As of March 31, 2020, there were approximately $7.2 million of unrecognized compensation costs, net of estimated forfeitures, related to stock option awards grants, which are expected to be recognized over a remaining weighted average period of 2.7 years.

RSUs

The following table presents a summary of the Company's outstanding RSU awards granted as of March 31, 2020 (in thousands except weighted average grant-date fair value):



	Restricted Stock Units		Weighted Average Grant-Date Fair Value
Outstanding, December 31, 2019	1,481		$	7.79
Awarded	19		$	6.35
Vested	(12	)	$	72.92
Forfeited	(87	)	$	4.79
Outstanding, March 31, 2020	1,401		$	7.40
Outstanding, Expected to vest	1,228		$	4.89

As of March 31, 2020, there were approximately $4.1 million of unrecognized compensation costs, net of estimated forfeitures, related to RSUs grants, which are expected to be recognized over a remaining weighted average period of 2.8 years.

ESPP

As of March 31, 2020, there were 838,182 shares available for future purchases under the ESPP. There were 43,581 shares of common stock issued under the ESPP during the three months ended March 31, 2020. Cash proceeds from ESPP purchases were $42 thousand during the three months ended March 31, 2020. There were 31,522 shares of common stock issued under the ESPP during the three months ended March 31, 2019. Cash proceeds from ESPP purchases were $42 thousand during the three months ended March 31, 2019.