STOCK-BASED COMPENSATION - SUMMARY OF PLANS (Details) - Stock options - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Shares
Options Outstanding at beginning of the period (in shares)	8,110,239
Granted (in shares)	116,050
Exercised (in shares)	(15,000)
Canceled (in shares)	(53,739)
Options Outstanding at the end of the period (in shares)	8,157,550	8,110,239
Options Vested and Expected to Vest at the end of the period (in shares)	8,110,040
Options Exercisable at the end of the period (in shares)	4,948,179
Shares Available for Grant under the 2008 Plan (in shares)	5,727,572
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 13.13
Granted (in dollars per share)	7.50
Exercised (in dollars per share)	2.80
Canceled (in dollars per share)	17.28
Options Outstanding at the end of the period (in dollars per share)	13.04	$ 13.13
Options Vested and Expected to Vest at the end of the period (in dollars per share)	13.00
Options Exercisable at the end of the period (in dollars per share)	$ 8.82
Weighted Average Remaining Contractual Term
Options Outstanding at the beginning of the period	6 years 6 months	6 years 8 months 12 days
Options Outstanding at the end of the period	6 years 6 months	6 years 8 months 12 days
Options Vested and Expected to Vest at the end of the period	6 years 6 months
Options Exercisable at the end of the period	5 years 2 months 12 days
Additional information
Weighted average grant-date fair value (in dollars per share)	$ 4.71