STOCK-BASED COMPENSATION (Stock Option Activity) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Options (in shares)
Options outstanding, beginning of period	5,823,536	6,296,709	6,595,136
Options granted	2,400,500	1,987,952	1,443,810
Options exercised	(1,171,097)	(2,156,898)	(1,552,742)
Options forfeited/cancelled	(214,193)	(304,227)	(189,495)
Options outstanding, end of period	6,838,746	5,823,536	6,296,709
Options vested and exercisable at December 31, 2014	2,406,016
Options expected to vest	4,074,226
Weighted Average Exercise Price (in dollars per share)
Options outstanding, beginning of period	$ 13.99	$ 7.51	$ 4.65
Options granted	$ 32.51	$ 23.60	$ 16.80
Options exercised	$ 9.05	$ 4.31	$ 3.53
Options forfeited/cancelled	$ 25.33	$ 11.50	$ 11.35
Options outstanding, end of period	$ 20.98	$ 13.99	$ 7.51
Options vested and exercisable at December 31, 2014	$ 9.83
Options expected to vest	$ 26.82
Aggregate Intrinsic Value
Options outstanding, beginning of period	$ 122,003	$ 66,682	$ 48,447
Options granted	36,584	22,543	1,877
Options exercised	(45,321)	(66,066)	(22,623)
Options forfeited/cancelled	(4,802)	(7,131)	(1,279)
Options outstanding, end of period	183,073	122,003	66,682
Options vested and exercisable at December 31, 2014	91,236
Options expected to vest	$ 85,274