SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2012

Accounting Policies [Abstract]

Schedule of stock-based compensation expense

	2012		2011		2010
Research and development	$	1,533	$	1,586	$	1,283
General and administrative		2,602		2,244		1,976
Total stock-based compensation expense	$	4,135	$	3,830	$	3,259

Schedule of fair value under the Black-Scholes model

	2012			2011			2010
Dividend yield(1)		0.0	%		0.0	%		0.0	%
Weighted average expected volatility factor(2)		67	%		64	%		64	%
Risk free interest(3)		0.6-0.8	%		1.0–2.2	%		1.4–2.3	%
Expected term, excluding options issued pursuant to the Employee Stock Purchase Plan(4)	5.9–7.0 years			5.6–6.4 years			5.9–6.4 years
Expected term—Employee Stock Purchase Plan(5)	6 months			6 months			6 months

(1) We have historically not paid dividends on our common stock and we do not anticipate paying any dividends in the foreseeable future.

(2) Measured using an average of historical daily price changes of our stock over a period equal to our expected term.

(3) 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.

(4) 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.

(5) The expected term of options issued in connection with our Employee Stock Purchase Plan is 6 months based on the terms of the plan.