Stock based compensation

6 Months Ended

Jun. 30, 2020

Stock based compensation

Stock based compensation

9. Stock-based compensation

Stock-Based Compensation Expense

Total compensation cost recognized for all stock-based compensation awards in the condensed consolidated statements of operations and comprehensive loss is as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
	(in thousands)
Research and development	$	1,764	$	3,256	$	3,449	$	4,671
General and administrative		2,095		1,998		4,451		4,100
Total stock-based compensation expense	$	3,859	$	5,254	$	7,900	$	8,771

Stock-based compensation expense by type of award included within the condensed consolidated statements of operations and comprehensive loss was as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
	(in thousands)
Stock options	$	2,930	$	4,528	$	6,138	$	7,304
Restricted stock awards and units		864		668		1,605		1,351
Employee stock purchase plan awards		65		58		157		116
Total stock-based compensation expense	$	3,859	$	5,254		7,900		8,771

Restricted Stock Units

A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the six months ended June 30, 2020 was as follows:

		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2019	455,404		12.16
Granted	448,929	$	12.83
Vested	(130,003)		11.02
Forfeited	(64,600)	$	10.66
Unvested restricted stock units as of June 30, 2020	709,730	$	12.93

Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and is recognized over the vesting period. The weighted average fair value of restricted stock units granted to employees during the three and six months ended June 30, 2020 was $8.05 and $12.83 per share, respectively. The weighted average fair value of restricted stock units granted to employees during the three and six months ended June 30, 2019 was $20.74 and $10.91 per share, respectively. The restricted stock units granted in the three and six months ended June 30, 2020 vest in equal amounts, annually over three years. The expense related to restricted stock units granted to employees was $0.9 million and $1.6 million for the three and six months ended June 30, 2020, respectively. The expense related to restricted stock units granted to employees was $0.7 million and $1.4 million for the three and six months ended June 30, 2019, respectively.

As of June 30, 2020, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $7.7 million, which is expected to be recognized over the remaining average vesting period of 2.3 years.

Stock Options

The following is a summary of stock option activity for the six months ended June 30, 2020:

		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2019	5,317,326	$	15.98
Granted	1,147,215	$	12.33
Exercised	(163,513)	$	10.31
Cancelled or forfeited	(407,853)	$	16.59
Outstanding at June 30, 2020	5,893,175	$	15.38	7.5	$	5,378
Exercisable at June 30, 2020	2,988,988	$	15.55	6.4	$	3,334

As of June 30, 2020, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $26.3 million which is expected to be recognized over the remaining weighted-average vesting period of 2.7 years.