STOCK-BASED COMPENSATION (Stock Option Activity) (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Options (in shares)
Options outstanding, beginning of period	4,901,748	6,637,239	7,450,914
Options granted	160,181	261,373	313,088
Options exercised	(945,166)	(1,789,434)	(895,804)
Options forfeited/cancelled	(32,569)	(200,210)	(227,759)
Options expired	(1,250)	(7,220)	(3,200)
Options outstanding, end of period	4,082,944	4,901,748	6,637,239
Options vested and exercisable as of December 31, 2018	3,183,103
Options expected to vest as of December 31, 2018	867,711
Weighted Average Exercise Price (in dollars per share)
Options outstanding, beginning of period	$ 40.91	$ 37.20	$ 34.07
Options granted	112.81	73.40	70.27
Options exercised	36.69	30.23	20.13
Options forfeited/cancelled	63.28	57.09	47.89
Options expired	25.72	4.63	1.52
Options outstanding, end of period	44.54	$ 40.91	$ 37.20
Options vested and exercisable as of December 31, 2018	36.10
Options expected to vest as of December 31, 2018	$ 73.93
Aggregate Intrinsic Value
Options outstanding, beginning of period	$ 326,064	$ 179,936	$ 331,938
Options outstanding, end of period	291,846	$ 326,064	$ 179,936
Options vested and exercisable as of December 31, 2018	254,360
Options expected to vest as of December 31, 2018	$ 36,539
Weighted Average Remaining Contractual Term (in years)
Options outstanding as of December 31, 2018	5 years 5 months 13 days
Options vested and exercisable as of December 31, 2018	4 years 11 months 4 days
Options expected to vest as of December 31, 2018	7 years 3 months 8 days