STOCK-BASED COMPENSATION, Stock Option Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Number of Options
Options outstanding at January 1, 2015	6,838,746
Options granted	2,069,300
Options exercised	(346,499)
Options forfeited/cancelled	(33,922)
Options outstanding at March 31, 2015	8,527,625
Options vested and exercisable at March 31, 2015	3,329,962
Options expected to vest	4,741,728
Weighted Average Exercise Price
Options outstanding at January 1, 2015	$ 20.98
Options granted	$ 61.38
Options exercised	$ 12.84
Options forfeited/cancelled	$ 28.22
Options outstanding at March 31, 2015	$ 31.09
Options vested and exercisable at March 31, 2015	$ 15.56
Options expected to vest	$ 40.53
Aggregate Intrinsic Value
Options outstanding at January 1, 2015	$ 183,073
Options granted	(186)
Options exercised	(16,788)
Options forfeited/cancelled	(1,122)
Options outstanding at March 31, 2015	257,534
Options vested and exercisable at March 31, 2015	152,279
Options expected to vest	$ 98,438