Share-based Compensation

During the year ended December 31, 2018, the Company granted awards under the 2018 Omnibus Incentive Compensation Plan, previously named the Amended and Restated 2009 Omnibus Incentive Compensation Plan (the “2018 Plan”), and the 2015 Incentive Compensation Plan (the “2015 Plan”). The Compensation Committee of the Board of Directors administers the plans.

Under the 2015 Plan and the 2018 Plan, a maximum of 4,000,000 shares and 18,523,000 shares, respectively, of common stock may be issued upon the exercise of stock options, in the form of restricted stock, or in settlement of RSUs or other awards, including awards with alternative vesting schedules such as performance-based criteria.

For the years ended December 31, 2018 and 2017, the following table presents total share-based compensation expense in each functional line item on the consolidated statements of operations (in thousands):



	Year Ended December 31,
	2018		2017
Cost of revenues	$	390	$	182
Research and development	1,017		749
Sales and marketing	970		747
General and administrative	2,499		1,901
Restructuring charges	—		169
Total	$	4,876	$	3,748

Stock Options

The Compensation Committee of the Board of Directors determines eligibility, vesting schedules and exercise prices for stock options granted. Stock options generally have a term of ten years and vest over a three- to four-year period.

The following table presents the weighted-average assumptions used in the Black-Scholes valuation model by the Company in calculating the fair value of each stock option granted:



	Year Ended December 31,
	2018		2017
Expected dividend yield	—	%	—	%
Risk-free interest rate	2.8	%	1.8	%
Volatility	84	%	108	%
Expected term (in years)	5.8		5.0

The weighted-average fair value of stock option awards granted during the years ended December 31, 2018 and 2017 was $1.56 and $0.89, respectively.

The following table summarizes the Company’s stock option activity for the years ended December 31, 2018 and 2017 (dollars in thousands, except per share data):



	Stock Options Outstanding		Weighted-Average Exercise Price Per Option		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding — December 31, 2017	6,566,483		$	1.77
Granted	5,106,892		2.18
Exercised	(1,611,731	)	1.25
Canceled	(1,265,432	)	1.80
Outstanding — December 31, 2018	8,796,212		$	2.10	8.44	$	19,124
Vested and Expected to Vest — December 31, 2018	7,407,752		$	2.10	8.25	$	16,269
Exercisable — December 31, 2018	2,748,498		$	2.30	6.46	$	6,145

During the year ended December 31, 2017, 146,039 shares were issued upon the exercise of stock options. The total intrinsic value of stock options exercised to purchase common stock during the years ended December 31, 2018 and 2017 was approximately $2.4 million and $0.1 million, respectively.

As of December 31, 2018, total unrecognized share-based compensation expense related to non-vested stock options was $5.5 million, which is expected to be recognized over a weighted-average period of approximately 2.8 years. The Company recognized approximately $2.5 million and $2.3 million of share-based compensation expense related to the vesting of stock option awards during the years ended December 31, 2018 and 2017, respectively.

Restricted Stock Units

Pursuant to the 2018 Plan and the 2015 Plan, the Company may issue RSUs that, upon satisfaction of vesting conditions, allow for recipients to receive common stock. Issuances of such awards reduce common stock available under the 2018 Plan and 2015 Plan for stock incentive awards. The Company measures compensation cost associated with grants of RSUs at fair value, which is generally the closing price of the Company’s stock on the date of grant. RSUs generally vest over a three- to four-year period.

A summary of restricted stock unit activity under all plans for the year ended December 31, 2018 is presented below:



	Number of Shares		Weighted-Average Grant-Date Fair Value
Non-vested — December 31, 2017	1,055,977		$	2.06
Granted	966,747		2.01
Vested	(1,110,138	)	1.96
Forfeited	(458,204	)	2.07
Non-vested — December 31, 2018	454,382		$	2.17

During the year ended December 31, 2017, the weighted-average grant-date fair value of RSUs granted was $1.83. During the years ended December 31, 2018 and 2017, the total fair value of shares vested was $2.1 million and $3.0 million, respectively.

As of December 31, 2018, there was $0.5 million of unrecognized share-based compensation expense related to non-vested RSUs, which is expected to be recognized over a weighted-average period of 1.6 years. The Company recognized approximately $2.2 million and $1.3 million of share-based compensation expense related to the vesting of RSUs during the years ended December 31, 2018 and 2017, respectively.

2000 Employee Stock Purchase Plan

The ESPP permits eligible employees of the Company to purchase newly issued shares of common stock, at a price equal to 85% of the lower of the fair market value on (i) the first day of the offering period or (ii) the last day of each six-month purchase period, through payroll deductions of up to 10% of their annual cash compensation. Under the ESPP, a maximum of 5,324,000 shares of common stock may be purchased by eligible employees.

During the years ended December 31, 2018 and 2017, the Company issued 282,101 shares and 232,038 shares, respectively, under the ESPP. The Company recognized approximately $0.2 million and $0.1 million of share-based compensation expense related to the ESPP during the years ended December 31, 2018 and 2017, respectively.