CASH, CASH EQUIVALENTS AND AVAILABLE-FOR-SALE SECURITIES (Tables)

9 Months Ended

Sep. 30, 2011

CASH, CASH EQUIVALENTS AND AVAILABLE-FOR-SALE SECURITIES

Schedule of fair value and amortized cost of cash, cash equivalents, and available-for-sale securities by major security type

Cash and cash equivalents	Amortized Cost		Estimated Fair Value		Gross Unrealized Gains		Gross Unrealized Losses
Cash and money market funds	$	71,479	$	71,479	$	—	$	—
Total cash and cash equivalents	$	71,479	$	71,479	$	—	$	—

Available-for-sale securities	Amortized Cost		Estimated Fair Value		Gross Unrealized Gains		Gross Unrealized Losses
U.S. Treasury securities	$	83,757	$	83,776	$	22	$	(3	)
Total available-for-sale securities	$	83,757	$	83,776	$	22	$	(3	)

As of December 31, 2010 (in thousands):

Cash and cash equivalents	Amortized Cost		Estimated Fair Value		Gross Unrealized Gains		Gross Unrealized Losses
Cash and money market funds	$	37,216	$	37,216	$	—	$	—
Total cash and cash equivalents	$	37,216	$	37,216	$	—	$	—

Available-for-sale securities	Amortized Cost		Estimated Fair Value		Gross Unrealized Gains		Gross Unrealized Losses
U.S. Treasury securities	$	101,966	$	101,970	$	12	$	(8	)
Total available-for-sale securities	$	101,966	$	101,970	$	12	$	(8	)

Summary of available-for-sale securities by maturity date

	Amortized Cost		Estimated Fair Value
Due within one year	$	83,757	$	83,776
	$	83,757	$	83,776

Summary of cash equivalent and available-for-sale securities in an unrealized loss position

	Less Than 12 Months
September 30, 2011	Gross Unrealized Losses			Estimated Fair Value
U.S. Treasury securities	$	(3	)	$	18,548

At December 31, 2010, the Company had the following cash equivalent and available-for-sale securities that were in an unrealized loss position (in thousands):

	Less Than 12 Months
December 31, 2010	Gross Unrealized Losses			Estimated Fair Value
U.S. Treasury securities	$	(8	)	$	42,822
Total	$	(8	)	$	42,822

Schedule of assets measured at fair value on a recurring basis

	Basis of Fair Value Measurements
	Balance at September 30, 2011		Level 1		Level 2		Level 3
Cash and cash equivalents:
Cash and money market funds	$	71,479	$	71,479	$	—	$	—
Total cash and cash equivalents	$	71,479	$	71,479	$	—	$	—

	Basis of Fair Value Measurements
	Balance at September 30, 2011		Level 1		Level 2		Level 3
Available-for-sale securities:
U.S. Treasury securities	$	83,776	$	83,776	$	—	$	—
Total available-for-sale securities	$	83,776	$	83,776	$	—	$	—
Reported as:
Cash and cash equivalents	$	71,479
Available-for-sale securities	83,776
Total	$	155,255

The following fair value hierarchy tables present information about the Company’s assets (cash and cash equivalents and available-for-sale securities) measured at fair value on a recurring basis as of December 31, 2010 (in thousands):

	Basis of Fair Value Measurements
	Balance at December 31, 2010		Level 1		Level 2		Level 3
Cash and cash equivalents:
Cash and money market funds	$	37,216	$	37,216	$	—	$	—
Total cash and cash equivalents	$	37,216	$	37,216	$	—	$	—

	Basis of Fair Value Measurements
	Balance at December 31, 2010		Level 1		Level 2		Level 3
Available-for-sale securities:
U.S. Treasury securities	$	101,970	$	101,970	$	—	$	—
Total available-for-sale securities	$	101,970	$	101,970	$	—	$	—
Reported as:
Cash and cash equivalents	$	37,216
Available-for-sale securities	101,970
Total	$	139,186