STOCK-BASED COMPENSATION

The following table summarizes the components of stock-based compensation expense recognized in the Company’s condensed consolidated statements of income and comprehensive income for the periods indicated:



	Three Months Ended March 31,
	2019		2018
Cost of revenues (exclusive of depreciation and amortization)	$	12,781	$	8,289
Selling, general and administrative expenses	9,075		8,307
Total	$	21,856	$	16,596

Stock Options

Stock option activity under the Company’s plans is set forth below:



	Number of Options		Weighted Average Exercise Price		Aggregate Intrinsic Value		Weighted Average Remaining Contractual Term (in years)
Options outstanding at January 1, 2019	4,082,944		$	44.54
Options granted	131,849		$	169.13
Options modified	17,871		$	163.55
Options exercised	(323,464	)	$	36.76
Options forfeited/cancelled	(2,624	)	$	61.38
Options outstanding at March 31, 2019	3,906,576		$	49.92	$	465,698	5.4

Options vested and exercisable at March 31, 2019	3,422,907		$	41.11	$	438,196	5.0
Options expected to vest at March 31, 2019	445,175		$	111.17	$	25,804	8.6

As of March 31, 2019, $17,097 of total remaining unrecognized stock-based compensation cost related to unvested stock options, net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 3.1 years.

Restricted Stock and Restricted Stock Units

Service-Based Awards

The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the three months ended March 31, 2019.



	Equity-Classified Restricted Stock			Equity-Classified Equity-Settled Restricted Stock Units				Liability-Classified Cash-Settled Restricted Stock Units
	Number of Shares	Weighted Average Grant Date Fair Value Per Share		Number of Shares		Weighted Average Grant Date Fair Value Per Share		Number of Shares		Weighted Average Grant Date Fair Value Per Share
Unvested service-based awards outstanding at January 1, 2019	793	$	63.10	797,903		$	92.13	302,967		$	83.99
Awards granted	—	$	—	242,783		$	168.95	48,632		$	169.13
Awards modified	—	$	—	6,897		$	170.74	668		$	168.36
Awards vested	—	$	—	(242,414	)	$	85.38	(102,902	)	$	80.55
Awards forfeited/cancelled	—	$	—	(9,769	)	$	91.07	(1,653	)	$	86.79
Unvested service-based awards outstanding at March 31, 2019	793	$	63.10	795,400		$	118.33	247,712		$	102.34

As of March 31, 2019, $32 of total remaining unrecognized stock-based compensation cost related to service-based equity-classified restricted stock is expected to be recognized over the weighted-average remaining requisite service period of 1.3 years.

As of March 31, 2019, $80,152 of total remaining unrecognized stock-based compensation cost related to service-based equity-classified restricted stock units (“RSUs”), net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 3.1 years.

As of March 31, 2019, $33,762 of total remaining unrecognized stock-based compensation cost related to service-based liability-classified RSUs, net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 2.5 years.

The liability associated with the service-based liability-classified RSUs as of March 31, 2019 and December 31, 2018, was $9,673 and $9,920, respectively, and was classified as Deferred compensation due to employees in the condensed consolidated balance sheets.

Performance-Based Awards

The table below summarizes activity related to the Company’s equity-classified performance-based awards for the three months ended March 31, 2019.



	Equity-Classified Equity-Settled Restricted Stock Units
	Number of Shares		Weighted Average Grant Date Fair Value Per Share
Unvested performance-based awards outstanding at January 1, 2019	29,592		$	121.75
Awards modified	(29,592	)	$	121.75
Unvested performance-based awards outstanding at March 31, 2019	—		$	—

During the first quarter of 2019, the Company and holders of the unvested performance-based equity-classified RSUs mutually agreed to cancel the performance-based RSU awards and the Company issued service-based stock option and RSU awards with four-year vesting terms to those same recipients. As of March 31, 2019, there is no remaining unrecognized stock-based compensation cost related to performance-based equity-classified RSUs.