Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2012

Cash Equivalents and Marketable Securities

Schedule of marketable securities

Marketable securities are summarized as follows (in thousands):

Balance at December 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses Less than 12 Months			Gross Unrealized Losses 12 Months or Longer		Aggregate Fair Value
Corporate debt securities	$	110,540	$	13	$	(45	)	$	—	$	110,508
US government debt securities		59,811		7		(3	)		—		59,815
Foreign government debt securities		2,415		6		—			—		2,421
Total	$	172,766	$	26	$	(48	)	$	—	$	172,744

Balance at December 31, 2011	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses Less than 12 Months			Gross Unrealized Losses 12 Months or Longer		Aggregate Fair Value
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

Schedule of contractual maturities of marketable securities

The following table summarizes the contractual maturities of marketable securities at December 31, 2012 (in thousands):

	Amortized Cost		Aggregate Fair Value
Matures in less than one year	$	111,184	$	111,192
Matures in one to three years		61,582		61,552
Total	$	172,766	$	172,744

Schedule of marketable securities with unrealized losses by contractual maturity dates

The following table summarizes marketable securities with unrealized losses by contractual maturity dates at December 31, 2012 (in thousands):

	Less than 12 Months					12 Months or Longer				Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Corporate debt securities	$	70,191	$	(45	)	$	—	$	—	$	70,191	$	(45	)
US government debt securities		24,215		(3	)						24,215		(3	)
Total	$	94,406	$	(48	)	$	—	$	—	$	94,406	$	(48	)