Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Schedule of fair value assumptions

The fair value of each option grant is estimated on the grant date using the Black-Scholes option-pricing model, and the following weighted average assumptions:

	Year Ended December 31,
	2019			2018
Estimated dividend yield	0.00		%	0.00		%
Expected volatility	102.14		%	81.73		%
Risk-free interest rate	1.87		%	2.75		%
Expected life of options (in years)	5.20			5.68
Weighted-average fair value per share	$	1.77		$	2.06

The fair value of the SARs was estimated using the Black-Scholes option-pricing model for the respective periods, using the following assumptions:

	July 31, 2019			December 31, 2018
Estimated dividend yield	—			—
Expected volatility	115.82		%	86.71		%
Risk-free interest rate	2.07		%	2.63		%
Expected term (years)	0.51			1.09
Fair value per share of common stock underlying the SAR	$	2.66		$	0.83
SAR exercise price	$	3.80		$	3.80

The fair value of the Performance Plan is estimated at each financial reporting date using the Monte Carlo simulation model and the following assumptions:

	December 31,
	2019			2018
Estimated dividend yield	—			—
Expected volatility	128.30		%	87.19		%
Risk-free interest rate	1.53		%	2.47		%
Expected term (years)	2.17			3.17
Fair value per share of common stock underlying the Performance Plan	$	0.86		$	0.83

Schedule of Share-based Compensation Expenses

Total share-based compensation expense included in the consolidated statements of operations is as follows:

	Year Ended December 31,
	2019		2018
Research and development	$	710	$	1,144
General and administrative	1,128		1,060
	$	1,838	$	2,204

Summary of Stock Option Activity

Stock option activity for the periods indicated is as follows:

	Shares Available for Grant		Shares Subject to Outstanding Options		Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Options outstanding as of December 31, 2017	1,023,378		1,399,484		$	7.17
Additional shares reserved under plan	—		—
Options granted	(626,757	)	727,257		2.97
Options forfeited	302,755		(403,748	)	7.61
Options exercised	—		(51,327	)	1.16
Options outstanding as of December 31, 2018	699,376		1,671,666		$	5.42
Options granted	(633,030	)	658,030		2.36
Options forfeited	322,117		(507,950	)	7.07
Options exercised	—		(32,443	)	2.12
Options outstanding as of December 31, 2019	388,463		1,789,303		$	3.89	8.03	$	638
Vested and expected to vest as of    December 31, 2018			1,585,689		$	5.53	8.11	$	2
Exercisable as of December 31, 2018			1,007,870		$	6.58	7.54	$	2
Vested and expected to vest as of    December 31, 2019			1,731,437		$	3.94	7.99	$	597
Exercisable as of December 31, 2019			1,032,801		$	4.81	7.20	$	190