STOCK-BASED EMPLOYEE COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Activity of unvested restricted stock units and performance share units

Restricted Stock Units and Performance Share Units

The following table summarizes the activity of restricted stock units and performance share units ("share-based awards") during the six months ended June 30, 2018: 

Share-Based Awards	Shares		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2017	524,696			$	1,431.88
Granted	153,637			$	2,035.68
Vested	(184,648	)		$	1,277.74
Performance Shares Adjustment	12,676			$	1,587.94
Forfeited/Canceled	(21,685	)		$	1,649.68
Unvested at June 30, 2018	484,676			$	1,676.34

Schedule of share-based compensation, stock options, activity

Stock Options

All outstanding employee stock options were assumed in acquisitions. The following table summarizes the activity for stock options during the six months ended June 30, 2018: 

Employee Stock Options	Number of Shares		Weighted-Average Exercise Price			Aggregate  Intrinsic Value (in thousands)			Weighted-Average Remaining Contractual Term (in years)
Balance, December 31, 2017	30,675			$	401.61		$	40,986	3.9
Exercised	(2,770	)		$	480.63
Forfeited	(13	)		$	241.83
Balance, June 30, 2018	27,892			$	393.92		$	45,552	3.3
Vested and exercisable at June 30, 2018	27,819			$	402.22		$	45,492	3.3
Vested and exercisable at June 30, 2018 and expected to vest thereafter	27,892			$	393.92		$	45,552	3.3