Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Allocated Stock-Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options and shares issued under the Company's 2017 Employee Stock Purchase Plan (2017 Plan) in the following expense categories of its accompanying consolidated statements of operations for the three and nine months ended September 30, 2020 and 2019:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Cost of product sales	$	25	$	33	$	113	$	78
Research and development	334		90		922		617
General and administrative	2,267		2,312		6,822		6,857
	$	2,626	$	2,435	$	7,857	$	7,552

Schedule of Stock Option Activity

The following table summarizes the activity related to stock option grants to employees and nonemployees for the nine months ended September 30, 2020:

	Shares	Weighted average exercise price per share		Weighted average remaining contractual life
Outstanding at December 31, 2019	7,399,217	$	9.81	6.37
Granted	1,303,210	5.64
Exercised	(71,748)	2.26
Expired	—	—
Forfeited	(472,927)	10.13
Outstanding at September 30, 2020	8,157,752	$	9.19	6.12
Exercisable at September 30, 2020	5,384,480	$	9.58	4.83
Vested and expected to vest at September 30, 2020	8,157,752	$	9.19	6.12

Schedule of Fair Value Options using Black-Scholes Pricing Model

The grant date fair value of each stock option grant was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions:

	Nine Months Ended September 30,
	2020			2019
Risk free interest rate	0.71		%	2.48		%
Expected term (in years)	6.03			6.05
Expected volatility	68.77		%	67.03		%
Annual dividend yield	0.00		%	0.00		%
Fair value of common stock	$	5.64		$	7.70

The Company calculated the fair value of each option grant and the shares issued under the 2017 Plan on the respective dates of grant using the following weighted average assumptions:

	Nine Months Ended September 30,
	2020		2019
Risk free interest rate	0.96	%	2.32	%
Expected term (in years)	0.5		0.5
Expected volatility	84.55	%	73.34	%
Annual dividend yield	0.00	%	0.00	%

Schedule of Nonvested Restricted Stock Units Activity

The following table summarizes the activity related to RSUs granted to employees for the nine months ended September 30, 2020:

	Shares
Balance at December 31, 2019	—
Granted	1,542,172
Vested and settled	—
Expired/forfeited/canceled	(42,716)
Balance at September 30, 2020	1,499,456
Expected to vest at September 30, 2020	1,499,456