Investments (Tables)

6 Months Ended

Jun. 30, 2012

Investments

Summary of contract maturity of available-for-sale securities

One year or less	66	%
After one year but within two years	24	%
After two years but within three years	10	%
Total	100	%

Summary of investments

								Other-Than-
								Temporary
	Amortized		Unrealized					Impairment			Estimated
June 30, 2012	Cost		Gains		Losses			Loss			Fair Value
Short-term investments:
Corporate debt securities	$	115,609	$	62	$	(45	)	$	—		$	115,626
Debt securities issued by U.S. government agencies	38,564		16		(3		)	—			38,577
Debt securities issued by states of the United States and political subdivisions of the states	11,930		6		(3		)	—			11,933
Total securities with a maturity of one year or less	166,103		84		(51		)	—			166,136
Corporate debt securities	49,671		32		(189		)	—			49,514
Debt securities issued by U.S. government agencies	13,660		22		(107		)	—			13,575
Debt securities issued by the U.S. Treasury	8,484		9		(3		)	—			8,490
Debt securities issued by states of the United States and political subdivisions of the states	12,636		42		(9		)	—			12,669
Total securities with a maturity of more than one year	84,451		105		(308		)	—			84,248
Subtotal	$	250,554	$	189	$	(359	)	$	—		$	250,384
Equity securities:
Current portion (included in Other current assets)	$	1,538	$	1,943	$	—		$	(880	)	$	2,601
Long-term portion (included in Deposits and other assets)	625		—		—			—			625
Subtotal	$	2,163	$	1,943	$	—		$	(880	)	$	3,226
	$	252,717	$	2,132	$	(359	)	$	(880	)	$	253,610

								Other-Than-
								Temporary
	Amortized		Unrealized					Impairment			Estimated
December 31, 2011	Cost		Gains		Losses			Loss			Fair Value
Short-term investments:
Corporate debt securities	$	109,842	$	13	$	(255	)	$	—		$	109,600
Debt securities issued by U.S. government agencies	53,723		35		(5		)	—			53,753
Debt securities issued by the U.S. Treasury	2,353		3		—			—			2,356
Debt securities issued by states of the United States and political subdivisions of the states	16,141		4		(3		)	—			16,142
Total securities with a maturity of one year or less	182,059		55		(263		)	—			181,851
Corporate debt securities	57,632		21		(331		)	—			57,322
Debt securities issued by U.S. government agencies	26,754		—		(67		)	—			26,687
Debt securities issued by states of the United States and political subdivisions of the states	12,331		19		(23		)	—			12,327
Total securities with a maturity of more than one year	96,717		40		(421		)	—			96,336
Subtotal	$	278,776	$	95	$	(684	)	$	—		$	278,187
Equity securities:
Current portion (included in Other current assets)	$	1,538	$	624	$	—		$	(880	)	$	1,282
Long-term portion (included in Deposits and other assets)	625		—		—			—			625
Subtotal	$	2,163	$	624	$	—		$	(880	)	$	1,907
	$	280,939	$	719	$	(684	)	$	(880	)	$	280,094

Schedule of investments temporarily impaired

		Less than 12 months of temporary impairment
	Number of Investments	Estimated Fair Value		Unrealized Losses
Corporate debt securities	37	$	80,812	$	(234	)
Debt securities issued by U.S. government agencies	6	14,572		(110		)
Debt securities issued by the U.S. Treasury	3	5,333		(3		)
Debt securities issued by states of the United States and political subdivisions of the states	2	6,548		(12		)
Total temporarily impaired securities	48	$	107,265	$	(359	)