STOCK-BASED COMPENSATION - Stock Option Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number		2,500,000	1,900,000
Cash received from option exercises	$ 1,468,000	$ 2,549,000	$ 8,611,000
Range of Option Exercise Price, Outstanding Options	6,837,006
Range of Option Exercise Price, Outstanding Options, Weighted Average Exercise Price	$ 7.65
Range of Option Exercise Price, Outstanding Options, Weighted Average Remaining Contractual Life	7 years 4 months 26 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	3,523,697
Range of Option Exercise Price, Exercisable Options, Weighted Average Exercise Price	$ 6.69
Unrecognized compensation expense	9,300,000
Total intrinsic value of options exercised	600,000	3,800,000	4,400,000
Range One
Equity Incentive Plans
Range of Option Exercise Price, Lower Limit	$ 1.71
Range of Option Exercise Price, Upper Limit	$ 4.24
Range of Option Exercise Price, Outstanding Options	409,250
Range of Option Exercise Price, Outstanding Options, Weighted Average Exercise Price	$ 2.73
Range of Option Exercise Price, Outstanding Options, Weighted Average Remaining Contractual Life	4 years 4 months 26 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	409,250
Range of Option Exercise Price, Exercisable Options, Weighted Average Exercise Price	$ 2.73
Range Two
Equity Incentive Plans
Range of Option Exercise Price, Lower Limit	$ 4.42
Range of Option Exercise Price, Upper Limit	$ 6.61
Range of Option Exercise Price, Outstanding Options	981,256
Range of Option Exercise Price, Outstanding Options, Weighted Average Exercise Price	$ 5.16
Range of Option Exercise Price, Outstanding Options, Weighted Average Remaining Contractual Life	5 years 8 months 15 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	932,756
Range of Option Exercise Price, Exercisable Options, Weighted Average Exercise Price	$ 5.12
Range Three
Equity Incentive Plans
Range of Option Exercise Price, Lower Limit	$ 6.62
Range of Option Exercise Price, Upper Limit	$ 6.65
Range of Option Exercise Price, Outstanding Options	1,681,000
Range of Option Exercise Price, Outstanding Options, Weighted Average Exercise Price	$ 6.63
Range of Option Exercise Price, Outstanding Options, Weighted Average Remaining Contractual Life	6 years 9 months 23 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	1,226,000
Range of Option Exercise Price, Exercisable Options, Weighted Average Exercise Price	$ 6.63
Range Four
Equity Incentive Plans
Range of Option Exercise Price, Lower Limit	$ 6.67
Range of Option Exercise Price, Upper Limit	$ 9.16
Range of Option Exercise Price, Outstanding Options	2,471,500
Range of Option Exercise Price, Outstanding Options, Weighted Average Exercise Price	$ 7.82
Range of Option Exercise Price, Outstanding Options, Weighted Average Remaining Contractual Life	8 years 7 months 9 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	524,334
Range of Option Exercise Price, Exercisable Options, Weighted Average Exercise Price	$ 8.27
Range Five
Equity Incentive Plans
Range of Option Exercise Price, Lower Limit	$ 11.04
Range of Option Exercise Price, Upper Limit	$ 16.63
Range of Option Exercise Price, Outstanding Options	1,294,000
Range of Option Exercise Price, Outstanding Options, Weighted Average Exercise Price	$ 12.08
Range of Option Exercise Price, Outstanding Options, Weighted Average Remaining Contractual Life	8 years 2 months 13 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	431,357
Range of Option Exercise Price, Exercisable Options, Weighted Average Exercise Price	$ 12.08
Stock Option
Equity Incentive Plans
Vesting period	3 years
Exercise period	10 years
Compensation expense	6,900,000	6,000,000	4,600,000
Expected volatility	61.00%	61.80%	64.80%
Risk-free interest rate	2.50%	2.13%	1.98%
Expected life of options	5 years 8 months 15 days	5 years 6 months 0 days	5 years 9 months 18 days
Dividend rate	0.00%	0.00%	0.00%
Fair value of options	$ 4.32	$ 6.24	$ 4.00
Balance at beginning of period, Options	5,732,821
Granted, Options	1,906,000
Exercised, Options	(272,622)
Forfeited and expired, Options	(529,193)
Balance at end of period, Options	6,837,006	5,732,821
Beginning Balance, Weighted Average Exercise Price	$ 7.59
Granted, Weighted Average Exercise Price	$ 7.68
Exercised, Weighted Average Exercise Price	$ 5.38
Forfeited and expired, Weighted Average Exercise Price	$ 8.33
Ending Balance, Weighted Average Exercise Price	$ 7.65	$ 7.59
Aggregate Intrinsic Value	4,150,000	6,185,000
Weighted Average Remaining Contractual Term	7 years 4 months 26 days	7 years 8 months 12 days
Outstanding options less expected forfeitures, Options	6,415,834
Outstanding options less expected forfeitures, Weighted Average Exercise Price	$ 7.56
Outstanding options less expected forfeitures, Aggregate Intrinsic Value	4,127,000
Outstanding options less expected forfeitures, Weighted Average Remaining Contractual Life	7 years 4 months 26 days
Exercisable, Options	3,523,697
Exercisable, Weighted Average Exercise Price	$ 6.69
Exercisable, Aggregate Intrinsic Value	$ 3,933,000
Exercisable, Weighted Average Remaining Contractual Life	6 years 2 months 13 days
Weighted-average period for unrecognized compensation expense	1 year 10 months 28 days
Minimum | Stock Option
Equity Incentive Plans
Exercise price (as a percent)	100.00%