Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2014

Schedule of shares of common stock reserved for issuance


Warrants to purchase common stock Options:		88,545
Outstanding under the 2012 Equity Incentive Plan		2,122,000
Outstanding under the 2001 Equity Incentive Plan		555,774
Available for future grants under the 2012 Equity Incentive Plan		1,218,925
Total common stock reserved for future issuance		3,985,244

Summary of stock option activity

The following table summarizes stock option activity for the year ended December 31, 2014:


				Weighted-
		Weighted-		Average
		Average		Remaining
		Exercise		Contractual	Aggregate
	Number of	Price		Term	Intrinsic Value
	Shares	(Per Share)(1)		(in years)	(in thousands)(2)
Balances at December 31, 2013	1,820,784	$	4.46
Options granted	1,298,500		4.24
Options forfeited	(258,969)		5.81
Options expired	(126,123)		5.49
Options exercised(3)	(56,418)		1.17
Balances at December 31, 2014	2,677,774		4.24	5.60	$	239
As of December 31, 2014:
Options vested and expected to vest(4)	2,407,005		4.22	5.56	$	234
Exercisable	1,172,747		3.93	5.05	$	215

(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 our common stock for in‑the‑money options at December 31, 2014.

(3)

The total intrinsic value of stock options exercised was $187,000, $787,000 and $607,000 for the years ended December 31, 2014, 2013 and 2012.

The stock options outstanding and exercisable by exercise price at December 31, 2014 are as follows:

Schedule of stock options outstanding and exercisable by exercise price


	Stock Options Outstanding		Stock Options Exercisable
		Weighted-
		Average	Weighted-			Weighted-
		Remaining	Average			Average
	Number of	Contractual Life	Exercise Price		Number of	Exercise Price
Range of Exercise Prices	Shares	In Years	Per Share		Shares	Per Share
$0.50 - $1.85	537,787	4.68	$	1.29	351,235	$	1.12
$1.87 - $4.74	644,987	6.05	$	3.41	255,641	$	3.68
$5.25 - $5.41	755,000	5.30	$	5.39	177,391	$	5.38
$5.57 - $6.00	710,000	6.10	$	5.93	374,730	$	5.95
$6.42 - $6.42	30,000	8.19	$	6.42	13,750	$	6.42
	2,677,774	5.60	$	4.24	1,172,747	$	3.93

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


	Year Ended December 31,
	2014	2013	2012
Expected term	6 years	6 years	6 years
Expected volatility	68 - 76%	57 - 59%	57 - 59%
Risk-free interest rate	1.8 - 1.9%	0.9 - 2.1%	0.8 - 1.4%
Expected dividend yield	0%	0%	0%

Schedule of total stock-based compensation expense recognized


	Year Ended December 31,
(In thousands)	2014		2013		2012
General and administrative	$	1,026	$	731	$	423
Research and development		987		709		398
	$	2,013	$	1,440	$	821