Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders' Equity Note [Abstract]

Schedule of shares of common stock reserved for issuance

The Company has reserved the following shares of common stock for issuance as of December 31, 2019:

Warrants to purchase common stock	331,193
Options:
Outstanding under the 2012 Equity Incentive Plan	15,881,406
Outstanding under the 2001 Equity Incentive Plan	315
Available for future grants under the 2012 Equity Incentive Plan	3,050,799
Shares reserved under the 2019 LPC Purchase Agreement	14,500,000
Total common stock reserved for future issuance	33,763,713

Summary of stock option activity

The following table summarizes stock option activity for the years ended December 31, 2019 and 2018:

	Number of Shares			Weighted Average Exercise Price (per share)(1)		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value ($000's) (2)
Outstanding at January 1, 2018		2,448,383		$	4.15
Granted		13,575,038			0.66
Cancelled (forfeited)		(572,935	)		3.20
Cancelled (expired)		(41,129	)		37.82
Outstanding at December 31, 2018		15,409,357			0.95
Granted		1,470,957			0.78
Exercised		(488,625	)		0.67
Cancelled (forfeited)		(509,923	)		0.62
Cancelled (expired)		(45	)		9.68
Outstanding at December 31, 2019		15,881,721		$	0.95		8.2	$	49
Options vested and expected to vest		15,827,723		$	0.95		8.2	$	49
Exercisable		13,661,670		$	0.99		8.0	$	22

(1) The weighted average price per share is determined using exercise price per share for stock options.

(2) The aggregate intrinsic value is calculated as the difference between the exercise price of the option and the fair value of the Company’s common stock for in-the-money options at December 31, 2019.

Schedule of stock options outstanding and exercisable by exercise price

The stock options outstanding and exercisable by exercise price at December 31, 2019 are as follows:

	Stock Options Outstanding					Stock Options Exercisable
Range of Exercise Prices		Number of Shares	Weighted- Average Remaining Contractual Life In Years		Weighted- Average Exercise Price Per Share		Number of Shares		Weighted- Average Exercise Price Per Share
$0.33 - $0.67		13,442,367	8.28	$	0.65		11,533,358	$	0.66
$0.84 - $1.30		755,080	9.15	$	1.09		445,705	$	0.94
$1.91 - $3.30		370,000	7.10	$	2.97		368,333	$	2.97
$3.38 - $3.38		1,263,022	6.71	$	3.38		1,263,022	$	3.38
$3.40 - $4.72		50,625	6.77	$	3.40		50,625	$	3.40
$8.24 - $17.36		315	1.02	$	12.94		315	$	12.94
$42.88 - $48.00		312	3.76	$	45.17		312	$	45.17
		15,881,721	8.17	$	0.95		13,661,670	$	0.99

Schedule of fair value-based measurement of stock options granted under the entity's stock plans estimated using Black-Scholes model

The weighted-average fair value-based measurement of stock options granted under the Company’s stock plans in the years ended December 31, 2019 and 2018 was $0.79 and $0.47 per share, respectively. The fair value- based measurement of stock options granted under the Company’s stock plans was estimated at the date of grant using the Black-Scholes model with the following assumptions:

	Year Ended December 31,
	2019	2018
Expected term	5 - 6 years	5 - 6 years
Expected volatility	96% - 99%	93% - 97%
Risk-free interest rate	1.74% - 2.59%	2.7% - 2.8%
Expected dividend yield	0%	0%

Schedule of total stock-based compensation expense recognized

Total expense for stock option grants recognized was as follows:

	Year ended December 31,
	2019		2018
General and administrative	$	1,928	$	4,611
Research and development		97		201
Total stock-based compensation	$	2,025	$	4,812