STOCK-BASED COMPENSATION, Stock Option Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Number of Options
Options outstanding at January 1, 2014	5,823,536
Options granted	2,346,500
Options exercised	(660,833)
Options forfeited/cancelled	(104,742)
Options outstanding at June 30, 2014	7,404,461
Options vested and exercisable at June 30, 2014	2,784,829
Options expected to vest	4,183,582
Weighted-Average Exercise Price
Options outstanding at January 1, 2014	$ 13.99
Options granted	$ 32.26
Options exercised	$ 8.29
Options forfeited/cancelled	$ 22.72
Options outstanding at June 30, 2014	$ 20.16
Options vested and exercisable at June 30, 2014	$ 9.74
Options expected to vest	$ 26.22
Aggregate Intrinsic Value
Options outstanding at January 1, 2014	$ 122,003
Options granted	26,961
Options exercised	23,433
Options forfeited/cancelled	2,203
Options outstanding at June 30, 2014	174,671
Options vested and exercisable at June 30, 2014	94,712
Options expected to vest	$ 73,338