Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

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, 2019	5,111,690	$	8.96	8.0	$	3,771
Granted	2,116,425		5.24
Exercised	(24,714)		1.70
Forfeited	(207,632)		12.64
Outstanding at September 30, 2019	6,995,769	$	7.76	7.8	$	1,429
Vested or expected to vest at September 30, 2019	6,995,769	$	7.76	7.8	$	1,429
Options exercisable at September 30, 2019	3,683,751	$	6.91	6.9	$	1,365

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

	Nine Months Ended September 30,
	2019			2018
Expected volatility	61%	–	82%	80%	–	85%
Risk-free interest rate	1.44%	–	2.58%	2.63%	–	2.96%
Expected dividend yield		0%			0%
Expected term (in years)	0.50	–	6.63	5.27	–	6.13

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

	September 30,	December 31,
	2019	2018
Warrant rights to acquire Common Stock	384,163	384,163
ESPP	561,971	223,341
Outstanding inducement stock option awards	673,500	498,000
2009 Plan	2,538,468	2,563,072
2017 Plan	4,485,323	3,130,910
Total	8,643,425	6,799,486

Schedule of stock based compensation expense

Stock-based Compensation Expenses—Stock‑based compensation expense was classified in the statements of operations as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
Cost of product revenues	$	60	$	–	$	101	$	–
Research and development		913		684		2,315		2,064
Selling, general and administrative		1,599		1,581		5,250		4,353
Total	$	2,572	$	2,265	$	7,666	$	6,417