Stock incentive plans (Tables)

9 Months Ended

Sep. 30, 2019

Stock incentive plans

Allocation of stock-based compensation expenses

Non-cash stock-based compensation expense recognized in the accompanying condensed statements of operations relating to both stock options, restricted stock awards and restricted stock units for the three and nine months ended September 30, 2019 and 2018 was as follows (in thousands):

	Three months ended				Nine months ended
	September 30,				September 30,
	2019		2018		2019		2018
Research and development	$	816	$	242	$	2,181	$	616
General and administrative		1,825		478		4,785		1,368
Total stock‑based compensation expense	$	2,641	$	720	$	6,966	$	1,984

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, 2018	3,959	$	7.46	8.79	$	35,984
Granted	1,663		12.77
Exercised	(142)		1.99
Forfeited and canceled	(522)		11.91
Outstanding, September 30, 2019	4,958	$	8.93	8.45	$	1,356
Vested and expected to vest at September 30, 2019	4,958	$	8.93	8.45	$	1,356
Exercisable at September 30, 2019	1,877	$	5.37	7.90	$	968

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, 2018	-	$	-
Issued	1,183	$	3.63
Vested	(2)		3.63
Forfeited and canceled	(26)		3.63
Unvested as of September 30, 2019	1,155	$	3.63