Stock-based awards (Tables)

9 Months Ended

Sep. 30, 2019

Stock-based awards

Schedule of assumptions used to determine grant-date fair value of stock options granted

	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2019			2018		2019			2018
Expected term (in years)		n/a		5.87			6.04		5.87
Volatility		n/a		70.86	%		69.80	%	70.86
Risk-free interest rate		n/a		2.86	%		2.39	%	2.86
Dividend yield		n/a		0.00	%		0.00	%	0.00
Weighted average fair value of common stock		n/a	$	0.29		$	8.26		0.29

Summary of stock option activity

		Weighted-		Weighted-
		Average		Average	Aggregate
		Exercise		remaining	Intrinsic
	Number	Price per		contractual	Value
	of Options	Share		term (years)	(000's)
Balance Outstanding, December 31, 2018	1,839,913	$	0.61	9.74	$	10,577
Options granted	1,228,352	$	7.61
Options exercised	(651,031)	$	0.65
Balance Outstanding, September 30, 2019	2,417,234	$	4.16	9.23	$	44,931
Exercisable, September 30, 2019	72,910	$	3.43	9.11	$	1,409
Vested and expected to vest, September 30, 2019	2,417,234	$	4.16	9.23	$	44,931