STOCK-BASED COMPENSATION (Details 2) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
STOCK-BASED COMPENSATION
Forfeiture rate (as a percent)	4.99%
Additional disclosures
Market price (in dollars per share)	$ 22.02
Total intrinsic value of options exercised	$ 400,000	$ 300,000
Weighted Average Grant Date Fair Value
Unrecognized compensation cost	42,300,000
Weighted average period for recognition of unrecognized compensation cost	3 years 3 months 18 days
Share based compensation expense	3,600,000	2,000,000
Stock Options [Member]
Valuation assumptions
Risk-free interest rates (as a percent)		1.96%
Risk-free interest rates, minimum (as a percent)	1.50%
Risk-free interest rates, maximum (as a percent)	1.92%
Expected term		6 years 3 months
Expected volatility (as a percent)		80.80%
Expected volatility, minimum (as a percent)	67.10%
Expected volatility, maximum (as a percent)	73.20%
Dividend yield (as a percent)	0.00%	0.00%
Weighted average fair value per share of options granted during the period (in dollars per share)	$ 15.81	$ 9.86
Shares
Outstanding at the beginning of the period (in shares)	4,934,317
Granted (in shares)	340,978
Exercised (in shares)	(28,375)
Forfeited (in shares)	(25,000)
Outstanding at the end of the period (in shares)	5,221,920		4,934,317
Exercisable at the end of the period (in shares)	4,419,801
Vested and expected to vest at the end of the period (in shares)	5,181,894
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 3.63
Granted (in dollars per share)	$ 23.51
Exercised (in dollars per share)	$ 10.72
Forfeited (in dollars per share)	$ 14.44
Outstanding at the end of the period (in dollars per share)	$ 4.83		$ 3.63
Exercisable at the end of the period (in dollars per share)	$ 2.66
Vested and expected to vest at the end of the period (in dollars per share)	$ 4.74
Weighted Average Remaining Contractual Term
Outstanding at the end of the period	5 years 2 months 12 days		5 years 2 months 12 days
Exercisable at the end of the period	4 years 7 months 6 days
Vested and expected to vest at the end of the period	5 years 2 months 12 days
Aggregate Intrinsic Value
Outstanding at the end of the period	90,249,000
Exercisable at the end of the period	85,576,000
Vested and expected to vest at the end of the period	$ 89,532,000
Stock Options [Member] | Minimum [Member]
Valuation assumptions
Expected term	6 years 3 months
Stock Options [Member] | Maximum [Member]
Valuation assumptions
Expected term	6 years 7 months 6 days
Restricted Stock Awards And Restricted Stock Units R S U [Member]
Restricted Shares
Outstanding at the beginning of the period (in shares)	1,541,114
Granted (in shares)	1,045,486
Released (in shares)	(237,061)
Forfeited (in shares)	(44,556)
Outstanding at the end of the period (in shares)	2,304,983
Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 13.86
Granted (in dollars per share)	$ 23.67
Released (in dollars per share)	$ 11.98
Forfeited (in dollars per share)	$ 14.01
Outstanding at the end of the period (in dollars per share)	$ 20.28