Short-Term Investments (Tables)

9 Months Ended

Sep. 30, 2011

Short-Term Investments [Abstract]

Schedule Of Summary Of Short-Term Investments

	Available-for-Sale Securities
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
September 30, 2011
U.S. Treasury securities	$	62,131	$	3	$	(5	)	$	62,129
Obligations of U.S. Government-sponsored enterprises		73,984		342		(99	)		74,227
Corporate debt securities		199,814		739		(189	)		200,364
Asset backed securities		1,710		—		(1	)		1,709
Total	$	337,639	$	1,084	$	(294	)	$	338,429
December 31, 2010
U.S. Treasury securities	$	46,234	$	4	$	—		$	46,238
Obligations of U.S. Government-sponsored enterprises		37,826		191		(50	)		37,967
Corporate debt securities		191,680		743		(23	)		192,400
Asset backed securities		1,531		6		—			1,537
Total	$	277,271	$	944	$	(73	)	$	278,142

Schedule Of Contractual Maturities Of Short-Term Investments

	Fair Value
Due within 1 year	$	247,370
After 1 but within 5 years		74,468
After 5 but within 10 years		—
After 10 years		16,591
Total	$	338,429

Schedule Of Gross Unrealized Losses And Fair Value Of Investments

	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
U.S. Treasury securities	$	23,341	$	(5	)	$	—	$	—		$	23,341	$	(5	)
Obligations of U.S Government-sponsored enterprises		46,142		(62	)		5,223		(37	)		51,365		(99	)
Corporate debt securities		71,324		(189	)		—		—			71,324		(189	)
Asset backed securities		569		(1	)		—		—			569		(1	)
	$	141,376	$	(257	)	$	5,223	$	(37	)	$	146,599	$	(294	)