Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of fair value of options granted

The weighted-average assumptions used in the Black-Scholes option-pricing model used to calculate the fair value of options granted during the year ended December 31, 2017, were as follows: 

	Employee			Non-Employee
Expected volatility		71.6% to 83.7	%		N/A
Expected dividend yield		—			N/A
Expected term (in years)		3.0 to 3.5			N/A
Risk-free interest rate		1.45% to 1.84	%		N/A

The weighted-average assumptions used in the Black-Scholes option-pricing model used to calculate the fair value of options granted during the year ended December 31, 2018, were as follows: 

	Employee			Non-Employee
Expected volatility		71.0% -79.8	%		N/A
Expected dividend yield		—			N/A
Expected term (in years)		3.0-3.5			N/A
Risk-free interest rate		1.58%-2.89	%		N/A

Schedule of stock option activity

The table summarizes the stock option activity, for both plans, for the periods indicated as follows: 

	Number of Options		Weighted Average Exercise Price Share		Weighted Average Remaining Contractual Per Term (years)	Aggregate Intrinsic Value (1)
Outstanding at December 31, 2016	1,477,300		$	1.61	5.8	$	9,662
Granted	258,500		$	4.62	5.0	$	34
Exercised	(18,000	)	$	0.50
Forfeited	(1,000	)	$	0.50
Expired	(65,000	)	$	10.22
Outstanding at December 31, 2017	1,651,800		$	1.67	3.7	$	—
Granted	179,471		$	1.53	4.4	$	—
Exercised	(49,000	)	$	0.50
Forfeited	(50,500	)	$	—
Expired	(10,600	)	$	—
Outstanding at December 31, 2018	1,721,171		$	1.57	4.0	$	—
Exercisable at December 31, 2018	1,443,296		$	1.56	3.5	$	—

(1) The aggregate intrinsic value on the table was calculated based on the difference between the estimated fair value of the Company’s stock and the exercise price of the underlying option. The estimated stock values used in the calculation was $0.59 and $0.72 per share for each of the years ended December 31, 2018 and 2017 respectively.

Schedule of stock-based compensation expense

The stock-based compensation expense was recorded as follows: 

	Years Ended December 31,
	2018		2017
Research and development	$	106	$	377
General and administrative		3,306		3,338
Total stock-based compensation expense	$	3,412	$	3,715

Schedule of summarizes restricted stock unit activity

The following table summarizes restricted stock unit activity for the years ended December 31, 2017 and 2016: 

	Number of  Units		Weighted Average Grant Date Fair Value Per Units
Outstanding as of December 31, 2016	455,430		$	0.76
Granted	117,885	(1)	$	6.95
Vested	(282,344	)	$	1.75
Forfeited	(3,086	)	$	—
Outstanding as of December 31, 2017	287,885		$	1.86
Granted	75,732	(2)	$	1.62
Vested	(223,795	)	$	2.56
Forfeited	(3,577	)	$	6.99
Outstanding as of December 31, 2018	136,345		$	0.98

(1) 40,000 restricted stock units were granted on March 27, 2017 with a weighted average grant date fair value of $8.35, 17,885 restricted stock units were granted on May 19, 2017 with a weighted average grant date fair value of $6.99 and 60,000 restricted stock units were granted on June 19, 2017 with a weighted average grant date fair value of $6.00.

(2) 12,820 restricted stock units were granted on June 12, 2017 with a weighted average grant date fair value of $0.65 and 62,912 restricted stock units were granted on June 12, 2018 with a weighted average grant date fair value of $1.82