Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2020

Equity [Abstract]

Fair Value Options Weighted-Average Assumptions

The fair value of options granted to employees and nonemployees was estimated using the Black-Scholes Option Pricing Method (see Note 2) with the following weighted-average assumptions used during the six months ended June 30:

	2020			2019
Dividend yield		0.0	%		0.0	%
Expected volatility		102.7	%		99.9	%
Risk-free interest rate		1.0	%		2.5	%
Expected life in years		5.80			5.76

Stock-based Compensation Expense

Stock-based compensation expense was as follows (in thousands):

	For the Three Months Ended				For the Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Stock-based compensation:
Options -
Selling, general, and administrative	$	963	$	1,952	$	1,883	$	4,938
Research and development		731		1,882		1,572		4,215
Restricted stock units -
Selling, general, and administrative		3,767		5,500		7,539		12,389
Research and development		5,169		6,106		8,543		12,036
Total stock-based compensation expense	$	10,630	$	15,440	$	19,537	$	33,578

Activity with Respect to Options Granted

Activity with respect to options granted under the 2011 Plan and 2017 Plan is summarized as follows:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2019		5,042,325		$	82.42		5.2	$	1,951
Granted		606,900		$	9.96		9.7
Forfeited		-		$	-
Exercised		(500	)	$	3.75			$	5
Expired		(476,087	)	$	92.81
Outstanding at June 30, 2020		5,172,638		$	72.97		5.5	$	3,723
Nonvested at June 30, 2020		944,433		$	13.49		9.4
Exercisable		4,228,205		$	86.25		4.6	$	2,329

Stock Options

	Shares			Weighted Average Grant-Date Fair Value
Nonvested shares at December 31, 2019		439,194			19.38
Granted		606,900			7.86
Vested/Issued		(101,661	)		32.46
Forfeited		-			-
Nonvested shares at June 30, 2020		944,433		$	10.57

Restricted Stock Units

	Shares			Weighted Average Grant-Date Fair Value
Nonvested shares at December 31, 2019		1,991,125		$	27.63
Granted		1,051,303			10.61
Vested/Issued		(423,113	)		41.43
Forfeited		(302,694	)		26.42
Nonvested shares at June 30, 2020		2,316,621		$	17.55