Stock incentive plan (Tables)

6 Months Ended

Jun. 30, 2020

Stock incentive plan

Allocation of stock-based compensation expenses

Non-cash stock-based compensation expense recognized in the accompanying condensed statements of operations relating to stock options, restricted stock awards, and restricted stock units for the three and six months ended June  30, 2020 and 2019 was as follows (in thousands):

	Three months ended				Six months ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	559	$	944	$	1,015	$	1,365
General and administrative		1,944		1,381		3,819		2,960
Total stock‑based compensation expense	$	2,503	$	2,325	$	4,834	$	4,325

Schedule of restricted stock unit activity

The table below summarizes activity related to restricted stock units (in thousands, except per share amounts):

		Weighted‑
		average
		grant date
		fair value
	Shares	per share
Unvested as of December 31, 2019	1,032	$	3.63
Issued	205	$	3.61
Vested	(21)		3.63
Forfeited and canceled	(85)		3.63
Unvested as of June 30, 2020	1,131	$	3.63

Summary of stock option activity

The table below summarizes activity related to stock options (in thousands, except per share amounts):

				Weighted‑
		Weighted‑		average
		average		remaining	Aggregate
		exercise		contractual	intrinsic
Options	Shares	price		term	value
Outstanding, December 31, 2019	4,798	$	8.75	8.29	$	1,159
Granted	2,375		3.12
Exercised	(203)		2.33
Forfeited and canceled	(290)		8.37
Outstanding, June 30, 2020	6,680	$	6.96	8.46	$	4,395
Vested and expected to vest at June 30, 2020	6,680	$	6.96	8.46	$	4,395
Exercisable at June 30, 2020	2,664	$	7.21	7.63	$	1,645