STOCK-BASED COMPENSATION, Stock Option Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Number of Options
Options outstanding at January 1, 2013	6,296,709
Options granted	1,931,500
Options exercised	(1,917,134)
Options forfeited/cancelled	(243,918)
Options outstanding at September 30, 2013	6,067,157
Options vested and exercisable at September 30, 2013	2,384,193
Options expected to vest	3,392,301
Weighted-Average Exercise Price
Options outstanding at January 1, 2013	$ 7.51
Options granted	$ 23.19
Options exercised	$ 4.07
Options forfeited/cancelled	$ 10.74
Options outstanding at September 30, 2013	$ 13.47
Options vested and exercisable at September 30, 2013	$ 6.03
Options expected to vest	$ 18.14
Aggregate Intrinsic Value
Options outstanding at January 1, 2013	$ 66,682
Options granted	21,845
Options exercised	(58,338)
Options forfeited/cancelled	(5,795)
Options outstanding at September 30, 2013	127,592
Options vested and exercisable at September 30, 2013	67,878
Options expected to vest	$ 55,498