STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Components of Stock-Based Compensation Expenses

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   June 30,				Six Months Ended   June 30,
	2019		2018		2019		2018
Cost of revenues (exclusive of depreciation and amortization)	$	7,480	$	7,054	$	20,261	$	15,343
Selling, general and administrative expenses	8,217		7,756		17,292		16,063
Total	$	15,697	$	14,810	$	37,553	$	31,406

Stock Options Activity

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	(528,572	)	$	42.52
Options forfeited/cancelled	(2,624	)	$	61.38
Options outstanding at June 30, 2019	3,701,468		$	49.83	$	456,287	5.2
Options vested and exercisable at June 30, 2019	3,232,985		$	40.60	$	428,366	4.7
Options expected to vest at June 30, 2019	435,976		$	112.48	$	26,427	8.4

Service-based Awards Activity

The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the six months ended June 30, 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	—	$	—	274,381		$	169.93	48,632		$	169.13
Awards modified	—	$	—	6,897		$	170.74	668		$	168.36
Awards vested	—	$	—	(255,903	)	$	86.05	(110,012	)	$	80.34
Awards forfeited/cancelled	—	$	—	(18,742	)	$	103.44	(2,648	)	$	91.52
Unvested service-based awards outstanding at June 30, 2019	793	$	63.10	804,536		$	121.01	239,607		$	103.10

Performance-based Awards Activity

The table below summarizes activity related to the Company’s equity-classified performance-based awards for the six months ended June 30, 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 June 30, 2019	—		$	—