Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

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 the 2005 Plan for the year ended December 31, 2019:

	2015 Plan			2005 Plan
		Weighted-			Weighted-
		Average			Average
	Stock	Exercise		Stock	Exercise
	Options	Price		Options	Price
Outstanding at January 1, 2019	2,392,567	$	62.41	582,616	$	65.72
Granted	1,620,721	$	5.98	—	$	—
Exercised	(1,514)	$	27.42	(1,500)	$	11.20
Canceled	(623,073)	$	61.29	(79,336)	$	76.42
Outstanding at December 31, 2019	3,388,701	$	35.64	501,780	$	64.19
Shares exercisable at December 31, 2019	1,017,774	$	80.55	501,780	$	64.19
Shares available for grant at December 31, 2019	228,335

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 and stock appreciation rights (not including awards that are subject to approval at the Company's annual meeting of stockholders in June 2020) granted under the 2015 Plan was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	2019		2018		2017
Weighted average Black-Scholes fair value of stock options and SARs granted		$4.98		$34.80		$21.20
Risk-free interest rate		1.5%-2.6%		2.3%-3.1%		1.6%-2.3%
Dividend yield		0%		0%		0%
Volatility		105.4%-134.1%		93.3%-115.6%		88.9%-114.1%
Expected term (in years)		3.9-7.5		4.1-7.5		4.1-7.5
Expected forfeiture rate		N/A		N/A		N/A

Schedule of summary of restricted stock units activity

The following is a summary of restricted stock units activity for the year ended December 31, 2019:

		Per Share
		Weighted-
	Number of	Average
	Shares	Fair Value
Outstanding and Unvested at January 1, 2019	―	$	―
Restricted stock units granted	1,251,609	$	6.43
Restricted stock units vested	(72,637)	$	10.40
Restricted stock units forfeited	(76,661)	$	9.61
Outstanding and Unvested at December 31, 2019	1,102,311	$	5.95

Schedule of stock-based compensation expense

The Company recorded stock-based compensation expense for awards issued under the above mentioned plans in the consolidated statements of operations as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Research and development	$	8,436	$	10,575	$	11,750
General and administrative		8,612		7,739		8,059
Total stock-based compensation expense	$	17,048	$	18,314	$	19,809

Employee Stock Option [Member]

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 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:

	2019		2018		2017
Range of Black-Scholes fair values of ESPP shares granted		$2.57-$35.00		$7.20-$70.64		$9.00-$109.40
Risk-free interest rate		1.2%-2.6%		0.7%-2.2%		0.4%-1.1%
Dividend yield		0%		0%		0%
Volatility		52.2%-171.6%		52.2%-203.8%		46.0%-267.8%
Expected term (in years)		0.5-2.0		0.5-2.0		0.5-2.0
Expected forfeiture rate		N/A		N/A		N/A