Stock Option Plans (Tables)

12 Months Ended

Dec. 31, 2019

Stock Option Plans

Summary of stock option activity

		Options Outstanding
			Weighted‑
	Shares		Average
	Available	Number of	Exercise
	for Grant	Options	Price
Balance at December 31, 2018	2,486,637	3,778,259	$	10.32
Additional shares authorized	1,170,000	—		—
Options granted	(2,029,000)	2,029,000		3.61
Options exercised	—	(87,303)		0.28
Options forfeited	76,546	(76,546)		11.67
Balance at December 31, 2019	1,704,183	5,643,410	$	8.05

Summary of information about stock options outstanding

			Options Outstanding				Options Vested
			at December 31, 2019				at December 31, 2019
				Weighted				Weighted
				Average				Average	Weighted
				Remaining	Weighted			Remaining	Average
				Contractual	Average			Contractual	Exercise
Exercise Price			Number	Life (in Years)	Exercise Price		Number	Life (in Years)	Price
$0.28	-	$2.56	191,000	5.66	$	0.36	184,730	5.52	$	0.29
$3.01	-	$4.65	2,027,500	9.75	$	3.61	32,375	6.01	$	4.64
$4.84		$7.59	1,061,522	8.94	$	5.95	261,504	8.90	$	5.98
$9.52	-	$14.43	1,051,738	7.98	$	10.83	593,596	7.93	$	10.90
$15.00	-	$16.70	1,311,650	6.51	$	15.49	1,138,764	6.44	$	15.40
			5,643,410	8.38	$	8.05	2,210,969	7.05	$	11.66

			Options Outstanding				Options Vested
			at December 31, 2018				at December 31, 2018
				Weighted				Weighted
				Average				Average	Weighted
				Remaining	Weighted			Remaining	Average
				Contractual	Average			Contractual	Exercise
Exercise Price			Number	Life (in Years)	Exercise Price		Number	Life (in Years)	Price
$0.28	-	$4.65	301,803	6.44	$	0.72	261,373	6.42	$	0.68
$5.94	-	$9.52	1,101,750	9.92	$	6.10	3,585	8.69	$	8.92
$9.60	-	$14.43	1,026,180	8.97	$	10.89	269,731	8.70	$	10.56
$15.00	-	$16.70	1,348,526	7.50	$	15.49	834,456	7.38	$	15.37
			3,778,259	8.52	$	10.32	1,369,145	7.46	$	11.60

Schedule of options outstanding and exercisable that had vested or were expected to vest

				Weighted
				Average	Aggregate
		Weighted		Remaining	Intrinsic
	Number	Average		Contractual	Value
	of shares	Exercise Price		Life (years)	(in thousands)
Vested	2,210,969	$	11.66	7.05	$	977,587
Expected to vest	3,432,441	$	5.72	9.24	$	3,713,778