FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2012

Dec. 31, 2011

Mar. 31, 2011

Dec. 31, 2011

FAIR VALUE MEASUREMENTS [Abstract]

Assets and liabilities carried at fair value measured on a recurring basis

The following table provides the assets carried at fair value measured on a recurring basis as of March 31, 2012 (in thousands):

			Fair Value Measurements, Using
	Total carrying value as of March 31, 2012		Quoted prices  in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	137,986	$	137,986	$	-	$	-
Short-term investments		194,331		194,331		-		-
Long-term investments		971		971		-		-

The following table provides the assets and liabilities carried at fair value measured on a recurring basis as of December 31, 2011 (in thousands):

			Fair Value Measurements, Using
	Total carrying  value as of December 31, 2011		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	96,538	$	96,538	$	-	$	-
Short-term investments		234,294		234,294		-		-

Reconciliation of the changes in fair value of the Company's stock warrant liability

The following table is a reconciliation of the changes in fair value of the Company's stock warrant liability for the three months ended March 31, 2011, which had been classified in Level 3 in the fair value hierarchy (in thousands):

	2011
Fair value of stock warrant liability, beginning of period	$	10,660
Loss for period		8,926
Warrants exercised		(6,476	)
Fair value of stock warrant liability, end of period	$	13,110

Valuation inputs using the Black-Scholes option pricing model

The fair value of the stock warrant liability was determined using the Black-Scholes option pricing model with the following inputs at March 31, 2011:

	2011
Contractual life (years)	0.4
Expected volatility	58.2%
Risk-free interest rate	0.1%
Annual dividend yield	-