Stock-based Compensation

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

7. Stock-based Compensation

The 2015 Stock Plan, as amended, is our primary plan through which equity based grants are awarded. We ceased making new awards under the 2006 Stock Plan upon adoption of the 2015 Stock Plan. The 2015 Stock Plan provides for the grant of incentive stock options,

non-statutory

stock options, restricted stock and other stock-based compensation awards to employees, officers, directors, and consultants of the Company. The administration of the 2015 Stock Plan is under the general supervision of the Compensation Committee of the Board of Directors. The terms of stock options awarded under the 2015 Stock Plan, in general, are determined by the Compensation Committee, provided the exercise price per share generally shall not be set at less than the fair market value of a share of the common stock on the date of grant and the term shall not be greater than ten years from the date the option is granted. As of June 30, 2020, the Company had options outstanding to purchase 1,820,142 shares of its common stock, which includes options outstanding under its 2006 Stock Plan. As of June 30, 2020, 984,220 shares were available for future issuance.

The following table summarizes stock option activity during the six months ended June 30, 2020:


	Shares			Weighted average exercise price
Outstanding at January 1, 2020		1,461,987		$	64.67
Options granted		381,125			88.04
Options exercised		(8,970	)		12.19
Options cancelled		(14,000	)		80.99

Outstanding at June 30, 2020		1,820,142		$	69.70

Exercisable at June 30, 2020		1,123,761		$	51.06

The total cash received by the Company as a result of stock option exercises was $0.1 million and $0.2 million, respectively, for the six months ended June 30, 2020 and 2019. The weighted-average grant date fair values, based on the Black-Scholes option model, of options granted during the six months ended June 30, 2020 and 2019 were $64.74 and $92.97, respectively.

Stock-Based Compensation Expense

Stock-based compensation expense during the six months ended June 30, 2020 and 2019 was as follows (in thousands):


	Three Months Ended June 30,				Six MonthsEndedJune 30,
	2020		2019		2020		2019
Stock-based compensation expense by type of award:
Stock options	$	5,689	$	7,632	$	10,535	$	13,533
Restricted stock		—		123		—		244

Total stock-based compensation expense	$	5,689	$	7,755	$	10,535	$	13,777

Effect of stock-based compensation expense by line item:
Research and development	$	2,289	$	2,366	$	4,367	$	4,243
General and administrative		3,400		5,389		6,168		9,534

Total stock-based compensation expense included in net loss	$	5,689	$	7,755	$	10,535	$	13,777

Unrecognized stock-based compensation expense on stock options as of June 30, 2020 was $44.6 million with a weighted average remaining period of 2.8 years.