Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2018

Stockholders' Equity Note [Abstract]

Schedule of shares of common stock reserved for issuance

The Company had reserved the following shares of common stock for issuance as of December 31, 2018:

Warrants to purchase common stock	331,193
Options:
Outstanding under the 2012 Equity Incentive Plan	15,408,997
Outstanding under the 2001 Equity Incentive Plan	360
Available for future grants under the 2012 Equity Incentive Plan	4,189,056
Total common stock reserved for future issuance	19,929,606

Summary of stock option activity

The following table summarizes stock option activity for the years ended December 31, 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, 2017		1,835,835		$	19.29
Granted		765,000			3.38
Cancelled (forfeited)		(152,365	)		5.86
Cancelled (expired)		(87	)		18.38
Outstanding at December 31, 2017		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		9.0	$	576
Options vested and expected to vest		15,356,965		$	0.95		9.0	$	574
Exercisable		10,283,026		$	1.01		9.0	$	379

(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, 2018.

Schedule of stock options outstanding and exercisable by exercise price

The stock options outstanding and exercisable by exercise price at December 31, 2018 are as follows:

	Stock Options Outstanding						Stock Options Exercisable
Range of Exercise Prices	Number of Shares		Weighted- Average Remaining Contractua l Life In Years		Weighted- Average Exercise Price Per Share		Number of Shares		Weighted- Average Exercise Price Per Share
$0.33 - $0.67		13,725,038		9.19	$	0.66		8,922,798	$	0.66
$1.91 - $3.30		370,000		8.10		2.97		361,666		2.97
$3.38 - $3.38		1,263,022		7.71		3.38		947,265		3.38
$3.40 - $4.72		50,625		7.77		3.40		50,625		3.40
$8.24 - $17.36		360		1.78		12.53		360		12.53
$42.88 - $48.00		312		4.76		45.17		312		45.17
		15,409,357		9.04	$	0.95		10,283,026	$	1.01

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

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,
	2018	2017
Expected term	5-6 years	5-6 years
Expected volatility	93% - 97%	83% - 88%
Risk-free interest rate	2.7 - 2.8%	1.8 - 2.1%
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,
	2018		2017
General and administrative	$	4,611	$	1,753
Research and development		201		362
	$	4,812	$	2,115