Note 7 - Stock-based Compensation

3 Months Ended

Mar. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

7. Stock-based Compensation

Stock Options

The following table summarizes stock option activity for employees and non-employees:

	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2014		1,235,526		$	4.19		7.1	$	7,709
Granted		399,929		$	10.61
Exercised		(236	)	$	1.27
Outstanding at March 31, 2015		1,635,219		$	5.76		7.6	$	9,632
Exercisable at March 31, 2015		593,324		$	2.38		4.4	$	5,505
Vested or expected to vest at March 31, 2015 (1)		1,526,587		$	5.65		7.4	$	9,153

(1) Represents the number of vested options at March 31, 2015 plus the number of unvested options expected to vest based on the unvested options outstanding at March 31, 2015.

Employee Stock Purchase Plan

The 2014 ESPP initially authorized the issuance of up to 140,500 shares of Common Stock. The number of shares increases each January 1, commencing on January 1, 2015 and ending on (and including) January 1, 2024, by an amount equal to the lesser of one percent of the outstanding shares as of the end of the immediately preceding fiscal year, 281,000 shares and any lower amount determined by the Company’s Board of Directors prior to each such January 1st. As of March 31, 2015, as a result of an increase on January 1, 2015 of one percent of the outstanding shares as of the end of the fiscal year ending December 31, 2014, the 2014 ESPP authorized the issuance of up to 304,991 shares of Common Stock. The first offering under the 2014 ESPP began on January 1, 2015. The Company incurred $11,000 in stock-based compensation expense related to the 2014 ESPP for the three months ended March 31, 2015.