6. Shareholders’ Equity

Equity Compensation Plans

We have a stock plan (the “Stock Plan”) and an inducement stock plan for newly hired employees (the “Inducement Plan”) (collectively, the “Plans”). Under the Plans, stock options to purchase shares of our common stock may be granted with a fixed exercise price that is equal to the fair market value of our common stock on the date of grant. These options have a term of up to 10 years and vest over a predetermined period, generally four years. Incentive stock options granted under the Stock Plan may only be granted to our employees. The Plans also allow for awards of non-qualified stock options, stock appreciation rights, RSAs and unrestricted stock awards, and RSUs. Expense is recorded for performance options over the requisite service periods when achievement of related performance targets are considered to be probable.

Stock-Based Compensation

The estimated fair value of stock-based awards is recognized as compensation expense over the vesting period of the award, net of estimated forfeitures. We estimate forfeitures based on historical experience and expected future activity. The fair value of RSUs is determined based on the number of shares granted and the quoted price of our common stock on the date of grant. The fair value of stock option awards is estimated at the grant date based on the fair value of each vesting tranche as calculated by the Black-Scholes-Merton (“BSM”) option-pricing model. The BSM model requires various highly judgmental assumptions including expected volatility and option life. If any of the assumptions used in the BSM model change significantly, stock-based compensation expense may differ materially in the future from that recorded in the current period. The fair values of our stock option grants were estimated with the following weighted average assumptions:

	Three Months Ended March 31,
	2016			2015
Dividend yield		0	%		0	%
Expected life	3.4 years			3.3 years
Expected volatility		55	%		53	%
Risk-free interest rate		1.1	%		1.2	%

The impact on our results of operations of stock-based compensation expense for the three month periods ended March 31, 2016 and 2015 was as follows (in thousands, except per share amounts):

	Three Months Ended March 31,
	2016		2015
Cost of revenue — service	$	138	$	113
Selling, general and administrative		249		138
Research and development		26		13
Total stock-based compensation expense	$	413	$	264
Per diluted share	$	0.03	$	0.02

Stock Option Activity

The following table summarizes stock option activity under the Plans for the three month period ended March 31, 2016:

Stock Options	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value
Balance at January 1, 2016		1,778,697		$	4.43
Granted		168,775			5.82
Exercised		(19,081	)		3.14
Forfeited		(15,843	)		5.79
Expired		(390	)		4.30
Balance at March 31, 2016		1,912,158		$	4.56		7.79	$	2,918,097
Vested and expected to vest at March 31, 2016		1,776,293		$	4.47		7.68	$	2,845,908
Exercisable at March 31, 2016		838,549		$	3.62		6.23	$	1,964,768

At March 31, 2016, total compensation cost related to stock options granted but not yet recognized was $1,431,216, net of estimated forfeitures. This cost will be amortized on the straight-line method over a weighted-average period of approximately 1.35 years. The following table summarizes certain information about stock options:

	Three Months Ended March 31,
	2016		2015
Weighted-average grant-date fair value of option grants for the period	$	3.06	$	2.34
Options in-the-money at period end		1,338,733		1,353,633
Aggregate intrinsic value of options exercised	$	49,330	$	47,880

The aggregate intrinsic value represents the difference between the exercise price of the underlying options and the quoted price of our common stock for the number of options that were in-the-money at period end or that were exercised during the period. We issue new shares of common stock upon exercise of stock options.

Restricted Stock Unit Activity

The following table summarizes RSU activity for the three month period ended March 31, 2016:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2016		104,463		$	5.97
Granted		2,500			5.83
Vested		(13,408	)		6.19
Forfeited		—			—
Unvested at March 31, 2016		93,555		$	5.94
Expected to vest after March 31, 2016		83,054		$	5.91

At March 31, 2016, total compensation cost related to RSUs granted but not yet recognized was $254,334, net of estimated forfeitures. This cost will be amortized on the straight-line method over a period of approximately 1.26 years.

Common Stock Reserved for Future Issuance

The following table summarizes our shares of common stock reserved for future issuance under the Plans as of March 31, 2016:

Stock options outstanding		1,912,158
RSUs outstanding		93,555
Stock awards available for future grant		865,435
Common stock reserved for future issuance		2,871,148