17. Stock incentive plans

In March 2011, our board of directors approved the 2011 Plan. The 2011 Plan provides for the grant of incentive and non-statutory stock options, stock appreciation rights, restricted shares of our common stock, stock units, and performance cash awards. As of December 31, 2018, 13,739,820 shares of common stock were reserved for issuance. As of December 31, 2018, options to purchase approximately 290,000 shares of common stock and RSUs covering approximately 3,119,000 shares of common stock were outstanding under the 2011 Plan.

No further awards will be made under our Amended and Restated 2001 Stock Incentive Plan, and it will be terminated. Options outstanding under the 2001 Plan will continue to be governed by their existing terms. As of December 31, 2018, options to purchase approximately 14,000 shares of common stock were outstanding under the 2001 Plan.

The following table summarizes our stock-based compensation expense included in the consolidated statements of operations for 2018, 2017 and 2016:


	Year Ended December 31,
	2018		2017		2016
Network operations	$	2,070	$	2,174	$	2,144
Development and technology		1,242		1,068		1,070
Selling and marketing		1,868		2,060		1,842
General and administrative		7,088		8,913		7,749
Total stock-based compensation expense	$	12,268	$	14,215	$	12,805

For the years ended December 31, 2018, 2017, and 2016, we capitalized $789, $696, and $727, respectively, of stock-based compensation expense to software and capital projects.

Stock option awards

We grant stock option awards to both employees and non‑employee directors. The grant date for these awards is the same as the measurement date. The stock option awards generally vest over a four-year service period with 25% vesting when the individual completes 12 months of continuous service and the remaining 75% vesting monthly thereafter. These awards are valued as of the measurement date and the stock‑based compensation expense, net of forfeitures, is recognized on a straight‑line basis over the requisite service period. A summary of the activity for stock option awards for 2018 is presented below:


		Weighted		Weighted-Average
	Number of	Average		Remaining	Aggregate
	Options	Exercise		Contract	Intrinsic
	(000’s)	Price		Life (years)	Value
Outstanding at December 31, 2017	1,283	$	9.58	3.8	$	16,573
Exercised	(972)	$	10.26
Canceled/forfeited	(7)	$	5.99
Outstanding and exercisable at December 31, 2018	304	$	7.49	3.8	$	3,970

The aggregate intrinsic value in the table above represents the difference between the estimated fair value of our common stock at December 31, 2018 and the option exercise price, multiplied by the number of in‑the‑money options at December 31, 2018. The intrinsic value changes are based on the estimated fair value of our common stock.

Stock options to purchase approximately 972,000, 1,776,000 and 532,000 shares of our common stock were exercised during the years ended December 31, 2018, 2017 and 2016 for cash proceeds of $9,979, $9,244 and $2,984, respectively. The total intrinsic value of stock options exercised for the years ended December 31, 2018, 2017 and 2016 was $14,935, $20,551 and $1,675, respectively.

Restricted stock unit awards

We grant time-based restricted stock units (“RSUs”) to executive and non-executive personnel and non-employee directors. The time-based RSUs granted to executive and non-executive personnel generally vest over a three-year period subject to continuous service on each vesting date. The time-based RSUs for our non-employee directors generally vest over a one-year period for existing members and 33.3% per year over a three‑year period for new members subject to continuous service on each vesting date.

We grant performance-based RSUs to executive personnel. These awards vest subject to certain performance objectives based on the Company’s revenue growth and/or Adjusted EBITDA growth achieved during the specified performance period and certain long-term service conditions. The maximum number of RSUs that may vest is determined based on actual Company achievement and performance-based RSUs generally vest over a three-year period subject to continuous service on each vesting date.

In 2016, our Compensation Committee determined to adjust its practice of making annual long-term equity grants and instead adopted a compensation cycle whereby it granted equity awards to our Chief Executive Officer and Chief Financial Officer covering the number of shares it might otherwise have granted in 2016 through 2018, with “cliff” vesting dates in 2019. These grants were made to focus our Chief Executive Officer and Chief Financial Officer on the Company’s overall long-term corporate and strategic goals, eliminate intervening quarterly vesting dates that force them to sell shares in the market to cover taxes triggered upon vesting, and strengthen the Company’s ability to retain our senior management team over the next three years. As a result of these larger-than-usual RSU grants, the Compensation Committee does not intend to grant additional equity awards to our Chief Executive Officer and Chief Financial Officer until 2019.

A summary of the RSU activity in 2018 is as follows:


		Weighted
	Number of	Average
	Shares	Grant Date
	(000’s)	Fair Value
Non-vested at December 31, 2017	3,324	$	7.35
Granted(2)	978	$	13.73
Vested	(1,113)	$	8.99
Canceled/forfeited	(70)	$	14.98
Non-vested at December 31, 2018	3,119	$	8.60

(2)

The RSUs granted to all of our named executive officers in 2016 were subject to satisfaction of specified service-based and performance-based conditions. The performance objectives were subject to under- or over- achievement on a sliding scale, with a threshold of 50% of the target number of RSUs and a maximum of 150% of the target RSUs. In February 2018, our Compensation Committee determined actual achievement of the 2016 performance-based RSUs resulting in additional RSUs granted of approximately 584,000 at a grant-date fair value of $6.13 per share during the year ended December 31, 2018.

During the year ended December 31, 2018, 1,112,938 shares of RSUs vested. The Company issued 702,447 shares and the remaining shares were withheld to pay minimum statutory federal, state, and local employment payroll taxes on those vested awards.

At December 31, 2018, the total remaining stock‑based compensation expense for unvested RSU awards is $9,314, which is expected to be recognized over a weighted average period of 2.6 years.