Employee Stock-Based Compensation

We currently grant restricted equity awards to employees and directors under our 2010 Equity Incentive Plan. Additionally, through our 2010 Employee Stock Purchase Plan, employees are able to purchase shares of our Class A common stock at a discount through payroll deductions. We have reserved shares of our Class A common stock for issuance under these plans.

Restricted Stock Units

The following table summarizes restricted stock units with only service conditions granted under our 2010 Equity Incentive Plan:



	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
	(In thousands, except per share data)
Restricted stock units granted	120		94		183		195
Weighted-average grant-date fair value	$	71.20	$	35.60	$	67.17	$	31.23

Note 8—Employee Stock-Based Compensation (continued)

Performance Based Restricted Stock Units

We grant performance-based restricted stock units to certain employees which are subject to the attainment of minimum pre-established annual performance targets. The majority of these awards are tied to the achievement of an annual non-GAAP earnings per share target for the grant year. The actual number of shares subject to the award is determined at the end of the annual performance period and may range from zero to 150% percent of the target shares granted. These awards contain an additional service component after each annual performance period is concluded and the unvested balance of the shares determined at the end of the annual performance period will vest over the remaining requisite service period. Compensation expense related to these awards is recognized using the accelerated attribution method over the four-year vesting period based on the fair value of the closing market price of our Class A common stock on the date of the grant and the estimated performance that is expected to be achieved. In the case of our Chief Executive Officer, vesting of the award is based on the achievement of a total shareholder return ("TSR") relative to the S&P 600 index over the three-year performance period. Compensation expense related to these awards is recognized over the performance period based on the grant date fair value through the use of a Monte Carlo simulation and are not subsequently re-measured.

The following table summarizes the performance-based restricted stock units granted under our 2010 Equity Incentive Plan:



	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
	(In thousands, except per share data)
Performance based restricted stock units granted ⁽¹⁾	168		329		612		616
Weighted-average grant-date fair value	$	71.47	$	36.35	$	49.04	$	36.01



(1	)	Performance awards granted also reflects the impact of any incremental shares awarded during the periods ended for performance periods completed. The grant date fair value for these awards are based on the grant price at the time of the initial award.

The total stock-based compensation expense recognized was $11.2 million and $9.9 million for the three months ended June 30, 2018 and 2017, respectively, and $20.6 million and $16.4 million for the six months ended June 30, 2018 and 2017, respectively. Total stock-based compensation expense includes amounts related to awards of stock options, restricted stock units (including performance-based restricted stock units) and purchases under our 2010 Employee Stock Purchase Plan.