Stock Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2020

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Weighted Average Assumptions Used

The estimated grant date fair values of employee stock option awards granted under the 2016 Plan and the 2018 Inducement Incentive Award Plan were calculated using the Black-Scholes option pricing model, based on the following weighted-average assumptions:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Risk-free interest rate	0.24		%	0.16		%	1.19		%	2.14		%
Dividend yield	—			—			—			—
Expected term	6.08			6.10			6.05			6.05
Expected volatility	94.88		%	88.23		%	90.19		%	87.79		%
Weighted-average fair value of common stock	$	2.47		$	1.70		$	2.39		$	2.17

Summary of Activity Under the 2008 Plan and the 2016 Plan

The following table summarizes the activity under the 2008 Plan, 2016 Plan, and 2018 Inducement Incentive Award Plan:

				Weighted-average
				remaining	Aggregate
	Number of	Weighted-average		contractual term	intrinsic value
	options	exercise price ($)		(in years)	(in thousands)
Employee awards
Outstanding at December 31, 2019	6,323,596	$	4.91	8.71	$	1,716
Granted	2,707,009	$	2.39
Exercised	(42,628)	$	2.42
Forfeited	(1,973,896)	$	4.73
Outstanding at September 30, 2020	7,014,081	$	4.01	8.57	$	1,873
Vested at September 30, 2020	1,907,100	$	7.04	7.32	$	273
Vested and expected to vest at September 30, 2020	6,521,522	$	4.13	8.51	$	1,739
Non-employee awards
Outstanding at December 31, 2019	473,073	$	5.89	6.23	$	38
Granted	—	$	—
Exercised	—	$	—
Forfeited	—	$	—
Outstanding at September 30, 2020	473,073	$	5.89	5.48	$	45
Vested at September 30, 2020	429,523	$	5.58	5.23	$	45
Vested and expected to vest at September 30, 2020	473,073	$	5.89	5.48	$	45

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award

The following table summarizes the status of the Company’s restricted stock units:

	Number of shares	Weighted average grant date fair value ($)
Unvested at December 31, 2019	181,250	$	5.00
Granted	—	—
Vested	82,812	6.03
Forfeited	—	—
Unvested at September 30, 2020	98,438	$	6.03

Schedule of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock

The Company recorded stock-based compensation expense related to stock option awards, restricted stock units and the ESPP in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Research and development	$	532	$	504	$	1,773	$	1,468
General and administrative	764		799		2,413		2,266
Total stock-based compensation expense	$	1,296	$	1,303	$	4,186	$	3,734