STOCK-BASED COMPENSATION - Plans by Exercise Price (Details)	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Options Outstanding | shares	6,543,162
Weighted Average Remaining Contractual Term	7 years 10 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 6.05
Number of Options Exercisable | shares	3,252,497
Weighted Average Exercise Price per Share (in dollars per share)	$ 4.33
$0.08 - $1.83
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower (in dollars per share)	0.08
Exercise price range, upper (in dollars per share)	$ 1.83
Number of Options Outstanding | shares	1,080,321
Weighted Average Remaining Contractual Term	4 years 6 months 8 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 1.00
Number of Options Exercisable | shares	1,077,605
Weighted Average Exercise Price per Share (in dollars per share)	$ 1.00
$2.05 - $5.61
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower (in dollars per share)	2.05
Exercise price range, upper (in dollars per share)	$ 5.61
Number of Options Outstanding | shares	918,658
Weighted Average Remaining Contractual Term	7 years 2 months 10 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 2.90
Number of Options Exercisable | shares	584,886
Weighted Average Exercise Price per Share (in dollars per share)	$ 2.15
$6.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price (in dollars per share)	$ 6.00
Number of Options Outstanding | shares	1,182,285
Weighted Average Remaining Contractual Term	5 years 7 months 28 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 6.00
Number of Options Exercisable | shares	907,365
Weighted Average Exercise Price per Share (in dollars per share)	$ 6.00
$6.09 - $6.85
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower (in dollars per share)	6.09
Exercise price range, upper (in dollars per share)	$ 6.85
Number of Options Outstanding | shares	245,000
Weighted Average Remaining Contractual Term	9 years 7 months 5 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 6.28
Number of Options Exercisable | shares	0
Weighted Average Exercise Price per Share (in dollars per share)	$ 0.00
$7.15
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price (in dollars per share)	$ 7.15
Number of Options Outstanding | shares	1,175,624
Weighted Average Remaining Contractual Term	9 years 11 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 7.15
Number of Options Exercisable | shares	156,240
Weighted Average Exercise Price per Share (in dollars per share)	$ 7.15
$7.48 - $11.31
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower (in dollars per share)	7.48
Exercise price range, upper (in dollars per share)	$ 11.31
Number of Options Outstanding | shares	1,941,274
Weighted Average Remaining Contractual Term	7 years 7 months 20 days
Weighted Average Exercise Price per Share (in dollars per share)	$ 9.68
Number of Options Exercisable | shares	526,401
Weighted Average Exercise Price per Share (in dollars per share)	$ 9.87