EQUITY AND SHARE-BASED COMPENSATION (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Number of Options
Outstanding at the beginning of the period (in shares)	3,058,309
Granted (in shares)	30,000	200,000
Exercised (in shares)	(16,450)
Outstanding at the end of the period (in shares)	3,071,859		3,058,309
Exercisable at the end of the period (in shares)	2,261,878
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 17.69
Granted (in dollars per share)	$ 88.56	$ 63.32
Exercised (in dollars per share)	$ 27.73
Outstanding at the end of the period (in dollars per share)	$ 18.32		$ 17.69
Exercisable at the end of the period (in dollars per share)	$ 12.20
Weighted average contractual term
Weighted average contractual term	5 years 10 months 24 days		6 years 1 month 6 days
Exercisable at the end of the period	5 years 3 months 18 days
Aggregate intrinsic value
Outstanding at the beginning of the period (in dollars)	$ 211,072
Outstanding at the end of the period (in dollars)	159,433		211,072
Exercisable at the end of the period (in dollars)	$ 130,326