Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2011

Cash Equivalents and Marketable Securities

Schedule of marketable securities

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses Less than 12 Months			Gross Unrealized Losses 12 Months or Longer		Aggregate Fair Value
Balance at December 31, 2011
Corporate debt securities	$	52,606	$	10	$	(11	)	$	—	$	52,605
US government debt securities		11,318		5		—			—		11,323
Foreign government debt securities		6,914		—		(17	)		—		6,897
Total	$	70,838	$	15	$	(28	)	$	—	$	70,825

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses Less than 12 Months			Gross Unrealized Losses 12 Months or Longer		Aggregate Fair Value
Balance at December 31, 2010
Corporate debt securities	$	22,597	$	6	$	(3	)	$	—	$	22,600
US government debt securities		47,466		12		(3	)		—		47,475
Total	$	70,063	$	18	$	(6	)	$	—	$	70,075

Schedule of contractual maturities of marketable securities

	Amortized Cost		Aggregate Fair Value
Matures in less than one year	$	69,921	$	69,908
Matures in one to three years		917		917
Total	$	70,838	$	70,825

Schedule of marketable securities with unrealized losses by contractual maturity dates

	Less than 12 months					Greater than 12 months				Total
	Fair Value		Gross Unrealized Losses			Fair Value		Net Unrealized Losses		Fair Value		Net Unrealized Losses
Corporate debt securities	$	30,811	$	(11	)	$	—	$	—	$	30,811	$	(11	)
Foreign government debt securities		6,914		(17	)						6,914		(17	)
Total	$	37,725	$	(28	)	$	—	$	—	$	37,725	$	(28	)