STOCK-BASED COMPENSATION - Stock Option Activity (Details) - Employee Stock Option $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Number of Options
Options outstanding at January 1, 2017 | shares	6,637,239
Options granted | shares	261,373
Options exercised | shares	(1,537,182)
Options forfeited/cancelled | shares	(142,491)
Options outstanding at September 30, 2017 | shares	5,218,939
Options vested and exercisable at September 30, 2017 | shares	3,303,812
Options expected to vest at September 30, 2017 | shares	1,838,657
Weighted Average Exercise Price
Options outstanding at January 1, 2017 | $ / shares	$ 37.20
Options granted | $ / shares	73.40
Options exercised | $ / shares	29.80
Options forfeited/cancelled | $ / shares	54.50
Options outstanding at September 30, 2017 | $ / shares	40.72
Options vested and exercisable at September 30, 2017 | $ / shares	31.32
Options expected to vest at September 30, 2017 | $ / shares	$ 56.64
Aggregate Intrinsic Value
Options outstanding at September 30, 2017 | $	$ 246,386
Options vested and exercisable at September 30, 2017 | $	187,029
Options expected to vest at September 30, 2017 | $	$ 57,532
Weighted Average Remaining Contractual Term (in years)
Options outstanding at September 30, 2017	6 years 5 months 16 days
Options vested and exercisable at September 30, 2017	5 years 9 months 11 days
Options expected to vest at September 30, 2017	7 years 7 months 9 days