Marketable Investments (Tables)

12 Months Ended

Dec. 31, 2012

Marketable Investments [Abstract]

Summary of the Company 's marketable investments

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Market Value
December 31, 2012
Available-for-sale securities
State and municipal obligations	$	18,859	$	27	$	(14	)	$	18,872
Federal agency and corporate obligations		115,653		380		(29	)		116,004
Total short-term available-for-sale securities		134,512		407		(43	)		134,876
ARS, long-term		11,000		—		(2,030	)		8,970
Total available-for-sale securities	$	145,512	$	407	$	(2,073	)	$	143,846
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Market 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 available for sale securities at their contractual maturity date

	FY 2013		FY2014		FY2015		Thereafter		Total
Federal agency and corporate obligations	$	50,403	$	44,727	$	20,874	$	—	$	116,004
State and municipal obligations		6,421		10,326		2,125		—		18,872
ARS		—		—		—		8,970		8,970
Total short and long-term	$	56,824	$	55,053	$	22,999	$	8,970	$	143,846

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

	As of December 31, 2012
	Less Than 12 Months				12 Months or Greater
	Market Value		Unrealized Losses		Market Value		Unrealized Losses
State and municipal bonds	$	9,430	$	14	$	—	$	—
Federal agency and corporate obligations		17,716		29		—		—
ARS		—		—		8,970		2,030
Total	$	27,146	$	43	$	8,970	$	2,030
	As of December 31, 2011
	Less Than 12 Months				12 Months or Greater
	Market Value		Unrealized Losses		Market Value		Unrealized 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 December 31, 2012
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	815	$	—	$	—	$	815
State and municipal obligations		—		18,872		—		18,872
Federal agency and corporate obligations (2)		—		148,117		—		148,117
ARS		—		—		8,970		8,970
Total	$	815	$	166,989	$	8,970	$	176,774
	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

Summary of changes in fair value of Level 3 financial assets

	ARS
Balance at December 31, 2010	$	9,117
Sales		—
Gains included in accumulated other comprehensive income (loss)		448
Balance at December 31, 2011		9,565
Sales		—
Losses included in accumulated other comprehensive income (loss)		(595	)
Balance at December 31, 2012	$	8,970