Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]

Schedule of summary of option activity

The following is a summary of stock options and stock appreciation rights activity under the 2015 Plan and 2005 Plan for the three months ended March 31, 2020:

	2015 Plan			2005 Plan
		Weighted-			Weighted-
		Average			Average
	Stock Options	Exercise Price		Stock Options	Exercise Price
Outstanding at January 1, 2020	3,388,701	$	35.64	501,780	$	64.19
Granted	22,086	$	6.52	—	$	—
Exercised	—	$	—	—	$	—
Canceled	(22,033)	$	37.44	(14,879)	$	47.85
Outstanding at March 31, 2020	3,388,754	$	35.46	486,901	$	64.69
Shares exercisable at March 31, 2020	1,098,087	$	77.97	486,901	$	64.69
Shares available for grant at March 31, 2020	219,732

Schedule of assumptions used to estimate grant date fair value of stock options and stock appreciation rights granted using black-scholes option-pricing model

The ESPP is considered compensatory for financial reporting purposes. As such, the fair value of ESPP shares was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended
	March 31,
	2020		2019
Range of Black-Scholes fair value of ESPP shares granted		$2.57-$35.00		$7.20-$34.80
Risk-free interest rate		1.5%-2.6%		1.2%-2.5%
Dividend yield		0%		0%
Volatility		66.6%-154.4%		52.2%-171.6%
Expected term (in years)		0.5-2.0		0.5-2.0
Expected forfeiture rate		0%		0%

Schedule of summary of restricted stock units activity

The following is a summary of restricted stock units activity for the three months ended March 31, 2020:

		Per Share
		Weighted-
		Average
	Number of	Grant-Date
	Shares	Fair Value
Outstanding and Unvested at January 1, 2020	1,102,311	$	5.95
Restricted stock units granted	25,000	$	7.95
Restricted stock units vested	(17,563)	$	8.76
Restricted stock units forfeited	(16,450)	$	5.95
Outstanding and Unvested at March 31, 2020	1,093,298	$	5.95

Schedule of stock-based compensation expense

The Company recorded all stock-based compensation expense in the consolidated statements of operations as follows (in thousands):

	Three Months Ended
	March 31,
	2020		2019
Research and development	$	1,908	$	3,179
General and administrative		2,057		2,379
Total stock-based compensation expense	$	3,965	$	5,558

Stock options

Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]

Schedule of assumptions used to estimate grant date fair value of stock options and stock appreciation rights granted using black-scholes option-pricing model

The fair value of stock options granted under the 2015 Plan was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended
	March 31,
	2020		2019
Weighted-average Black-Scholes fair value of stock options granted		$5.39		$27.60
Risk-free interest rate		0.6%-1.5%		2.4%-2.6%
Dividend yield		0%		0%
Volatility		133.6%-142.6%		111.7%-126.8%
Expected term (in years)		3.9		4.1-4.5
Expected forfeiture rate		0%		0%