SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - The fair value of stock options and employee stock purchase plan shares Valuaton assumptions (Details 1) (Stock Options)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years 10 months 24 days	[1]	5 years 7 months 6 days	[1]	5 years 10 months 24 days	[1]
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	7 years	[1]	6 years 4 months 24 days	[1]	6 years 4 months 24 days	[1]
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%	[2]	0.00%	[2]	0.00%	[2]
Weighted average expected volatility factor	67.00%	[3]	64.00%	[3]	64.00%	[3]
Expected term	6 months	[4]	6 months	[4]	6 months	[4]
Employee stock purchase plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest	0.60%	[5]	1.00%	[5]	1.40%	[5]
Employee stock purchase plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest	0.80%	[5]	2.20%	[5]	2.30%	[5]

[1] The expected term is the number of years that we estimate, based on historical experience, that options will be outstanding before exercise or cancellation. The range in expected term is the result of certain groups of employees exhibiting different exercising behavior.

[2] We have historically not paid dividends on our common stock and we do not anticipate paying any dividends in the foreseeable future.

[3] Measured using an average of historical daily price changes of our stock over a period equal to our expected term.

[4] The expected term of options issued in connection with our Employee Stock Purchase Plan is 6 months based on the terms of the plan.

[5] The risk-free interest rate for periods equal to the expected term of share option based on the U.S. Treasury yield in effect at the time of grant.