Stock-Based Compensation and Warrants (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Activity Under Stock Incentive Plans

A summary of activity under the stock incentive plans is as follows (in thousands, except share data and price per share):

	Shares Subject to Outstanding Options			Weighted- Average Exercise Price Per Share		Aggregate Intrinsic Value
Outstanding — Balance at December 31, 2019		661,701		$	21.60	$	305
Options granted		430,468			4.45
Options exercised		—			—
Options forfeited		(59,624	)		5.35
Options expired		(35,930	)		52.51
Outstanding — Balance at June 30, 2020		996,615		$	14.05	$	39
Vested and expected to vest — June 30, 2020		980,424		$	14.19	$	37
Exercisable —June 30, 2020		508,518		$	22.18	$	2

Weighted-Average Fair Value Assumption of Stock Option Awards

The fair value of stock option awards to employees, executives, directors, and other service providers was estimated at the date of grant using the Black-Scholes Model with the following weighted-average assumption. There were 430,468 and 184,071 options granted during the six months ended June 30, 2020 and 2019, respectively.

	Three Months Ended June 30,				Six Months Ended June 30,
		2020		2019		2020		2019
Expected term (years)		7.69		7.34		6.57		7.14
Expected volatility	112%		97%		119%		99%
Risk-free interest rate	0.54%		2.04%		1.12%		2.06%
Dividend yield		—		—		—		—