STOCK-BASED COMPENSATION (Details 3) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended								3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2009	Sep. 30, 2013 Option Plan Shares	Sep. 30, 2012 Option Plan Shares	Sep. 30, 2013 Option Plan Shares	Sep. 30, 2012 Option Plan Shares	Dec. 31, 2012 Option Plan Shares	Sep. 30, 2012 Option Plan Shares Maximum	Sep. 30, 2013 Option Plan Shares Maximum	Sep. 30, 2012 Option Plan Shares Maximum	Sep. 30, 2012 Option Plan Shares Minimum	Sep. 30, 2013 Option Plan Shares Minimum	Sep. 30, 2012 Option Plan Shares Minimum	Sep. 30, 2013 ESPP Shares	Sep. 30, 2012 ESPP Shares	Sep. 30, 2013 ESPP Shares Maximum	Sep. 30, 2012 ESPP Shares Maximum	Sep. 30, 2013 ESPP Shares Minimum	Sep. 30, 2012 ESPP Shares Minimum	Mar. 31, 2013 Restricted stock and restricted stock unit	Mar. 31, 2012 Restricted stock and restricted stock unit	Sep. 30, 2013 Restricted stock and restricted stock unit	Dec. 31, 2012 Restricted stock and restricted stock unit
STOCK-BASED COMPENSATION
Forfeiture rate (as a percent)			2.76%	1.38%
Valuation assumptions
Risk-free interest rates (as a percent)						1.73%
Risk-free interest rates, minimum (as a percent)														0.81%	0.94%	0.81%					0.11%	0.19%
Risk-free interest rates, maximum (as a percent)											0.89%	1.73%	0.89%						0.20%	0.27%
Expected term						6 years	6 years	6 years	6 years										2 years	2 years	6 months	6 months
Expected volatility (as a percent)						82.90%	86.00%
Expected volatility, minimum (as a percent)															82.90%	86.00%					39.10%	40.00%
Expected volatility, maximum (as a percent)												84.00%	92.00%						45.60%	55.00%
Dividend yield (as a percent)						0.00%	0.00%	0.00%	0.00%
Weighted average fair value per share of options granted during the period (in dollars per share)						$ 10.34	$ 7.47	$ 8.12	$ 6.90								$ 2.80	$ 3.47
Shares
Outstanding at the beginning of the period (in shares)								6,181,996
Granted (in shares)								290,570															180,750	262,500
Exercised (in shares)								(234,544)
Forfeited (in shares)								(129,625)
Outstanding at the end of the period (in shares)						6,108,397		6,108,397		6,181,996
Exercisable at the end of the period (in shares)						5,237,044		5,237,044
Vested and expected to vest at the end of the period (in shares)						6,057,354		6,057,354
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)								$ 2.62
Granted (in dollars per share)								$ 11.36
Exercised (in dollars per share)								$ 5.17
Forfeited (in dollars per share)								$ 10.15
Outstanding at the end of the period (in dollars per share)						$ 2.78		$ 2.78		$ 2.62
Exercisable at the end of the period (in dollars per share)						$ 1.79		$ 1.79
Vested and expected to vest at the end of the period (in dollars per share)						$ 2.74		$ 2.74
Weighted Average Remaining Contractual Term
Outstanding at the end of the period								6 years 6 months		6 years 7 months 6 days
Exercisable at the end of the period								5 years 8 months 12 days
Vested and expected to vest at the end of the period								6 years 6 months
Aggregate Intrinsic Value
Outstanding at the end of the period						$ 55,277,000		$ 55,277,000
Exercisable at the end of the period						52,461,000		52,461,000
Vested and expected to vest at the end of the period						55,142,000		55,142,000
Additional disclosures
Market price (in dollars per share)						$ 11.80		$ 11.80
Total intrinsic value of options exercised						1,000,000	400,000	1,600,000	3,800,000
Restricted Shares
Outstanding at the beginning of the period (in shares)																							813,955		813,955
Granted (in shares)																									998,102
Released (in shares)																									(188,981)
Forfeited (in shares)																									(358,981)
Outstanding at the end of the period (in shares)																									1,264,095	813,955
Unrecognized compensation cost	14,400,000		14,400,000
Weighted average period for recognition of unrecognized compensation cost			2 years 8 months 19 days
Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)																							$ 8.51		$ 8.51
Granted (in dollars per share)																									$ 11.80
Released (in dollars per share)																									$ 9.06
Forfeited (in dollars per share)																									$ 9.45
Outstanding at the end of the period (in dollars per share)																									$ 10.76	$ 8.51
Stock-based compensation	1,800,000	1,500,000	5,660,000	4,024,000																			(600,000)			600,000
Number of shares of common stock covered by warrants issued in connection with a consulting agreement					75,000
Expense related to stock warrants			$ 0
Exercise price (in dollars per share)	$ 0.01		$ 0.01