Note 6 − Stock-Based Compensation

The following tables summarize information about stock options and RSUs outstanding at December 31, 2018:

Options Outstanding							Options Vested and Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price
$ 0.24- 1.58		653,816		0.26	$	1.16		653,816		0.26	$	1.16
$ 1.74- 6.95		4,091,396		7.86		4.04		1,947,678		6.90		4.24
$ 14.52- 35.25		1,253,625		3.71		23.16		1,253,625		3.71		23.16
		5,998,837		6.16	$	7.72		3,855,119		4.74	$	9.87

The following tables summarize activity under the Plan for the indicated periods:

	Options
	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Outstanding at December 31, 2015		4,999,928		$	8.76		—	$	—
Options granted		429,000			4.77		—		—
Options exercised		(50,357	)		0.40		—		—
Outstanding at December 31, 2016		5,378,571		$	8.52		—	$	—
Options granted		1,613,500			4.06		—		—
Options exercised		(12,500	)		1.74		—		—
Options cancelled		(1,841,505	)		4.71		—		—
Outstanding at December 31, 2017		5,138,066		$	8.41		—	$	—
Options granted		1,095,000			3.52		—		—
Options exercised		(117,229	)		1.15		—		—
Options cancelled		(117,000	)		5.34		—		—
Outstanding at December 31, 2018		5,998,837		$	7.72		6.16	$	810
Options exercisable at December 31, 2018		3,855,119		$	9.87		4.74	$	809

	RSUs
	Number of RSUs			Weighted Average Grant Date Fair Value		Aggregate Intrinsic Value
Outstanding at December 31, 2015		359,956		$	13.22	$	—
RSUs granted		219,331			4.75		—
RSUs vested		(155,852	)		15.27		—
Outstanding at December 31, 2016		423,435		$	8.08	$	—
RSUs granted		220,664			3.83		—
RSUs vested		(174,438	)		10.47		—
Outstanding at December 31, 2017		469,661		$	5.19	$	—
RSUs granted		246,663			3.26		—
RSUs vested		(211,330	)		6.19		—
Outstanding at December 31, 2018		504,994		$	3.83	$	—

Intrinsic value is calculated as the difference between the per-share market price of our common stock on the last trading day of 2018, which was $2.40, and the exercise price of the options. For options exercised, the intrinsic value is the difference between market price and the exercise price on the date of exercise. We received cash proceeds of $135, $22 and $20 from stock options exercised in 2018, 2017 and 2016, respectively. The total intrinsic value of options exercised was $46, $25 and $91 during the years ended December 31, 2018, 2017 and 2016, respectively.

Stock-based compensation expense is included in general and administrative expense for each period as follows:

Stock-Based Compensation by Type of Award	Year Ended December 31, 2018		Year Ended December 31, 2017		Year Ended December 31, 2016
Stock options	$	2,926	$	2,446	$	3,436
RSUs		1,129		1,540		1,962
Total stock-based compensation expense	$	4,055	$	3,986	$	5,398

As of December 31, 2018, there was $5,960 of unrecognized stock-based compensation expense related to unvested employee stock options and $1,442 of unrecognized stock-based compensation expense related to unvested RSUs. These costs are expected to be recognized over a weighted-average period of 2.67 and 2.38 years, respectively.

The fair value of each option grant was estimated on the date of grant using the Black-Scholes option pricing model using the following weighted average assumptions:

	Year Ended December 31, 2018			Year Ended December 31, 2017			Year Ended December 31, 2016
Expected stock price volatility		85.26	%		84.91	%		79.6	%
Risk-free interest rate		2.73	%		1.94	%		1.85	%
Expected life term	6.02 years			6.08 years			6.03 years
Expected dividends		0	%		0	%		0	%

Based on the Black-Scholes option pricing model, the weighted average estimated fair value of employee stock options granted was $2.58, $2.93 and $3.25 per share during the years ended December 31, 2018, 2017 and 2016, respectively.

The expected life was determined using the simplified method outlined in ASC 718, “Compensation - Stock Compensation”. Expected volatility of the stock options was based upon historical data and other relevant factors. We have not provided an estimate for forfeitures because we have had nominal forfeited options and RSUs and believed that all outstanding options and RSUs at December 31, 2018, would vest.