STOCKHOLDERS' EQUITY (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compensation cost related to unvested stock awards not yet recognized
Compensation cost not yet recognized, net of estimated forfeitures (in dollars)	$ 8,344,000
Period for recognition of compensation cost on weighted average basis	35 months
Purchase Plan
Assumptions used to estimate fair value of awards
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected volatility range, minimum (as a percent)	45.80%	27.80%	46.80%
Expected volatility range, maximum (as a percent)	77.40%	58.40%	99.50%
Risk-free interest rate range, minimum (as a percent)	0.06%	0.10%	0.18%
Risk-free interest rate range, maximum (as a percent)	0.21%	0.32%	0.54%
Weighted average estimated fair value of purchase rights (in dollars per share)	$ 0.59	$ 1.20	$ 1.92
Purchase Plan | Minimum
Assumptions used to estimate fair value of awards
Expected term	6 months	6 months	6 months
Purchase Plan | Maximum
Assumptions used to estimate fair value of awards
Expected term	12 months	12 months	12 months
Stock options
Assumptions used to estimate fair value of awards
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected volatility range, minimum (as a percent)	63.10%	62.90%	62.50%
Expected volatility range, maximum (as a percent)	74.00%	66.00%	63.50%
Risk-free interest rate range, minimum (as a percent)	0.81%	0.88%	1.11%
Risk-free interest rate range, maximum (as a percent)	1.25%	2.37%	2.65%
Expected term	6 years	5 years	5 years
Weighted average estimated fair value of employee stock options granted (in dollars per share)	$ 0.89	$ 2.06	$ 2.87