Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Stock-based Compensation

Summary of option activity for employee and non employee awards

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Shares	Price		Term	Value
				(Years)	(in thousands)
Outstanding at January 1, 2020	7,453,076	$	7.46	7.7	$	1,313
Granted	1,469,422		3.85
Exercised	(61,158)		2.71
Forfeited	(43,397)		6.36
Outstanding at March 31, 2020	8,817,943	$	6.90	7.9	$	30,866
Vested or expected to vest at March 31, 2020	8,817,943	$	6.90	7.9	$	30,866
Options exercisable at March 31, 2020	4,441,194	$	7.14	6.9	$	15,609

Schedule of assumptions used in determining fair value of the stock options granted

	Three Months Ended March 31,
	2020			2019
Expected volatility	79%	–	80%	81%	–	82%
Risk-free interest rate	1.46%	–	1.73%	2.49%	–	2.56%
Expected dividend yield		0%			0%
Expected term (in years)	5.90	–	6.08	5.52	–	6.63

Schedule of stock based compensation expense

	Three Months Ended
	March 31,
	2020		2019
Cost of product revenues	$	20	$	2
Research and development		723		607
Selling, general and administrative		1,754		1,864
Total	$	2,497	$	2,473

Schedule of reserved common stock shares upon exercise of rights under equity compensation plans

	March 31,	December 31,
	2020	2019
Warrant rights to acquire Common Stock	384,163	384,163
ESPP	523,860	438,307
Outstanding inducement stock option awards	709,500	705,500
2009 Plan	2,439,678	2,530,586
2017 Plan	5,904,299	4,429,849
Total	9,961,500	8,488,405