Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity Award Activity

The activity related to equity awards, which are comprised of stock options, during the year ended December 31, 2020 is summarized as follows:

	Equity Awards			Weighted- average Exercise Price per Share		Weighted- average Remaining Contractual Term(1) (years)		Aggregate Intrinsic Value(2)
Outstanding at December 31, 2019		5,616,840		$	19.50
Granted		3,458,513		$	4.61
Exercised		(94,219	)	$	6.42
Cancelled/forfeited		(4,859,468	)	$	18.34
Outstanding at December 31, 2020		4,121,666		$	8.67		8.48	$	7,792
Exercisable at December 31, 2020		1,072,061		$	18.37		5.95	$	1,544

⁽¹⁾ Represents the weighted-average remaining contractual term of stock options.

⁽²⁾ Aggregate intrinsic value represents the product of the number of equity awards outstanding or equity awards exercisable multiplied by the difference between the Company’s closing stock price per share on the last trading day of the period, which was $3.88 as of December 31, 2020, and the exercise price.

Stock Options, Valuation Assumptions

The Company estimates the fair value of each stock option grant on the grant date using the Black-Scholes option-pricing model (the “Black-Scholes model”) with the following assumptions:

	Year Ended December 31,
	2020			2019
Expected volatility		93	%		97	%
Expected term (years)		6.07			6.05
Risk-free interest rate		0.7	%		2.5	%
Dividend yield	-			-

Share-based Compensation Expense

The classification of share-based compensation expense is summarized as follows (in thousands):

	Year Ended
	December 31,
	2020		2019
Selling, general and administrative	$	2,808	$	8,872
Research and development		3,399		14,861
Total share-based compensation expense	$	6,207	$	23,733