Stock based compensation (Tables)

6 Months Ended

Jun. 30, 2020

Stock based compensation

Compensation cost recognized for all stock-based compensation awards

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

Summary of stock-based compensation expense by classification

	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

Summary of status and changes in unvested restricted stock

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

Summary of status and changes in 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