Marketable Investments (Tables)

9 Months Ended

Sep. 30, 2012

Marketable Investments [Abstract]

Summary of the Company 's marketable investments

			Gross		Gross
	Amortized		Unrealized		Unrealized			Market
	Cost		Gains		Losses			Value
September 30, 2012
Available-for-sale securities
State and municipal obligations	$	19,051	$	30	$	(5	)	$	19,076
Federal agency and corporate obligations		128,190		495		(4	)		128,681
Total short-term available-for-sale securities		147,241		525		(9	)		147,757
ARS, long-term		11,000		—		(1,211	)		9,789
Total available-for-sale securities	$	158,241	$	525	$	(1,220	)	$	157,546
			Gross		Gross
	Amortized		Unrealized		Unrealized			Market
	Cost		Gains		Losses			Value
December 31, 2011
Available-for-sale securities
State and municipal obligations	$	9,485	$	9	$	(12	)	$	9,482
Federal agency and corporate obligations		127,717		127		(335	)		127,509
Total short-term available-for-sale securities		137,202		136		(347	)		136,991
ARS, long-term		11,000		—		(1,435	)		9,565
Total available-for-sale securities	$	148,202	$	136	$	(1,782	)	$	146,556

Summary of Auction Rate Securities at their contractual maturity date

	FY 2012		FY2013		FY2014		Thereafter		Total
State and municipal obligations	$	—	$	6,477	$	10,442	$	2,157	$	19,076
Federal agency and corporate obligations		12,223		48,514		46,962		20,982		128,681
ARS		—		—		—		9,789		9,789
Total	$	12,223	$	54,991	$	57,404	$	32,928	$	157,546

Summary of the gross unrealized losses and market value of available-for-sale securities with unrealized losses

	As of September 30, 2012
	Less Than 12 Months				12 Months or Greater
	Market		Unrealized		Market		Unrealized
	Value		Losses		Value		Losses
State and municipal bonds	$	9,531	$	5	$	—	$	—
Federal agency and corporate obligations		6,437		4		—		—
ARS		—		—		9,789		1,211
Total	$	15,968	$	9	$	9,789	$	1,211
	As of December 31, 2011
	Less Than 12 Months				12 Months or Greater
	Market		Unrealized		Market		Unrealized
	Value		Losses		Value		Losses
State and municipal bonds	$	2,763	$	9	$	1,107	$	3
Federal agency and corporate obligations		68,962		313		2,043		22
ARS		—		—		9,565		1,435
Total	$	71,725	$	322	$	12,715	$	1,460

Summary of Company's fair value hierarchy for its financial assets

	As of September 30, 2012
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	2,246	$	—	$	—	$	2,246
State and municipal obligations		—		19,076		—		19,076
Federal agency and corporate obligations (2)		—		138,777		—		138,777
ARS		—		—		9,789		9,789
Total	$	2,246	$	157,853	$	9,789	$	169,888
	As of December 31, 2011
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	5,786	$	—	$	—	$	5,786
State and municipal obligations		—		9,482		—		9,482
Federal agency and corporate obligations (2)		—		128,509		—		128,509
ARS		—		—		9,565		9,565
Total	$	5,786	$	137,991	$	9,565	$	153,342

(1) Included in cash and cash equivalents.

(2) $10.1 million and $1.0 million included in cash and cash equivalents at September 30, 2012 and December 31, 2011, respectively, as original maturities at the time of purchase were 90 days or less.

Summary of changes in fair value of Level 3 financial assets

	ARS
Balance at December 31, 2011		9,565
Sales		—
Total unrealized gains (losses):
Included in other comprehensive income (loss)		224
Balance at September 30, 2012	$	9,789
	ARS
Balance at December 31, 2010		9,117
Sales		—
Total unrealized gains (losses):
Included in other comprehensive income (loss)		422
Balance at September 30, 2011	$	9,539