STOCK-BASED COMPENSATION, Stock Option Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Number of Options
Options outstanding at January 1, 2014	5,823,536
Options granted	2,311,000
Options exercised	(323,592)
Options forfeited/cancelled	(58,741)
Options outstanding at March 31, 2014	7,752,203
Options vested and exercisable at March 31, 2014	3,008,362
Options expected to vest	4,269,150
Weighted-Average Exercise Price
Options outstanding at January 1, 2014	$ 13.99
Options granted	$ 32.14
Options exercised	$ 6.75
Options forfeited/cancelled	$ 18.17
Options outstanding at March 31, 2014	$ 19.67
Options vested and exercisable at March 31, 2014	$ 9.76
Options expected to vest	$ 25.72
Aggregate Intrinsic Value
Options outstanding at January 1, 2014	$ 122,003
Options granted	1,756
Options exercised	(8,462)
Options forfeited/cancelled	(865)
Options outstanding at March 31, 2014	102,562
Options vested and exercisable at March 31, 2014	69,613
Options expected to vest	$ 30,670