STOCK-BASED COMPENSATION - Stock Option Activity (Details) - Employee Stock Option $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 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	(1,277,952)
Options forfeited/cancelled | shares	(112,646)
Options outstanding at June 30, 2017 | shares	5,508,014
Options vested and exercisable at June 30, 2017 | shares	3,522,106
Options expected to vest at June 30, 2017 | shares	1,890,939
Weighted Average Exercise Price
Options outstanding at January 1, 2017 | $ / shares	$ 37.20
Options granted | $ / shares	73.40
Options exercised | $ / shares	29.57
Options forfeited/cancelled | $ / shares	55.98
Options outstanding at June 30, 2017 | $ / shares	40.30
Options vested and exercisable at June 30, 2017 | $ / shares	30.97
Options expected to vest at June 30, 2017 | $ / shares	$ 56.54
Aggregate Intrinsic Value
Options outstanding at June 30, 2017 | $	$ 241,196
Options vested and exercisable at June 30, 2017 | $	187,094
Options expected to vest at June 30, 2017 | $	$ 52,095
Weighted Average Remaining Contractual Term (in years)
Options outstanding at June 30, 2017	6 years 7 months 17 days
Options vested and exercisable at June 30, 2017	5 years 11 months 25 days
Options expected to vest at June 30, 2017	7 years 9 months 2 days