14. 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 January 1st of each year, the number of shares of common stock reserved for issuance under the 2011 Plan shall automatically be increased by a number equal to the lesser of (a) 4.5% of the total number of shares of common stock then outstanding, (b) 3,000,000 shares of common stock or (c) as determined by our board of directors. As of December 31, 2017, 13,739,820 shares of common stock were reserved for issuance. As of December 31, 2017, options to purchase 5,229,486 shares of common stock and 7,713,459 RSUs have been granted under the 2011 Plan.

At the 2015 Annual Meeting of Stockholders held on June 12, 2015, our stockholders approved the following amendments to our 2011 Equity Incentive Plan: (a) termination of the automatic "evergreen" share reserve increase feature after January 2018, so that no additional automatic annual share increases will occur thereafter; (b) remove the discretion to re-price any stock award; (c) implement more conservative "share counting" provisions, so that the following shares will no longer be available for subsequent issuance: (i) shares applied to pay the exercise price of an option, (ii) shares not otherwise issued in connection with the stock settlement of stock appreciation rights, (iii) shares used to satisfy tax withholding obligations relating to any stock award, and (iv) shares reacquired by us using cash proceeds from the exercise of options; and (d) ensure that certain awards are intended to qualify as performance-based compensation under Section 162(m) of the Internal Revenue Code.

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, 2017, options to purchase 154,699 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 2017, 2016 and 2015:

	Years ended December 31,
	2017		2016		2015
Network operations	$	2,174	$	2,144	$	1,504
Development and technology		1,068		1,070		731
Selling and marketing		2,060		1,842		3,411
General and administrative		8,913		7,749		3,752

Total stock-based compensation expense	$	14,215	$	12,805	$	9,398

For the years ended December 31, 2017, 2016, and 2015, we capitalized $696, $727, and $778, respectively, of stock-based compensation expense.

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 2017 is presented below:

	Number of Options (000's)			Weighted Average Exercise Price		Weighted-Average Remaining Contract Life (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2016		3,084		$	7.04		3.8	$	17,145
Exercised		(1,776	)	$	5.21
Canceled/forfeited		(25	)	$	6.56

Outstanding at December 31, 2017		1,283		$	9.58		3.8	$	16,573


Exercisable at December 31, 2017		1,282		$	9.58		3.8	$	16,560

The aggregate intrinsic value in the table above represents the difference between the estimated fair value of our common stock at December 31, 2017 and the option exercise price, multiplied by the number of in-the-money options at December 31, 2017. The intrinsic value changes are based on the estimated fair value of our common stock.

Stock options to purchase approximately 1,776,000, 532,000 and 440,000 shares of our common stock were exercised during the years ended December 31, 2017, 2016 and 2015 for cash proceeds of $9,244, $2,984 and $1,373, respectively. The total intrinsic value of stock options exercised for the years ended December 31, 2017, 2016 and 2015 was $20,551, $1,675 and $2,214, 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 25% per year over a four-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. We recognize stock-based compensation expense for performance-based RSUs when we believe that it is probable that the performance objectives will be met.

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 2017 is as follows:

	Number of Shares (000's)			Weighted Average Grant Date Fair Value
Non-vested at December 31, 2016		3,825		$	6.55
Granted		617		$	13.00
Vested		(974	)	$	7.57
Canceled/forfeited		(144	)	$	8.84

Non-vested at December 31, 2017		3,324		$	7.35

During the year ended December 31, 2017, 974,094 shares of RSUs vested. The Company issued 656,767 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, 2017, the total remaining stock-based compensation expense for unvested RSU awards is $13,391, which is expected to be recognized over a weighted average period of 2.8 years.