Investments (Tables)

12 Months Ended

Dec. 31, 2011

Investments

Summary of contract maturity of available-for-sale securities

The following table summarizes the contract maturity of the available-for-sale securities we held as of December 31, 2011:

One year or less	65	%
After one year but within two years	29	%
After two years but within three years	6	%
Total	100	%

Summary of investments

								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

								Other-Than-
								Temporary
	Amortized		Unrealized					Impairment			Estimated
December 31, 2010	Cost		Gains		Losses			Loss			Fair Value
Short-term investments:
Corporate debt securities	$	196,010	$	294	$	(41	)	$	—		$	196,263
Debt securities issued by U.S. government agencies	119,890		53		(34		)	—			119,909
Debt securities issued by the U.S. Treasury	24,030		10		—			—			24,040
Debt securities issued by states of the United States and political subdivisions of the states	6,989		3		—			—			6,992
Total securities with a maturity of one year or less	346,919		360		(75		)	—			347,204
Corporate debt securities	47,842		167		(44		)	—			47,965
Debt securities issued by U.S. government agencies	7,139		4		(11		)	—			7,132
Total securities with a maturity of more than one year	54,981		171		(55		)	—			55,097
Subtotal	$	401,900	$	531	$	(130	)	$	—		$	402,301
Equity securities:
Current portion (included in Other current assets)	$	1,538	$	1,353	$	—		$	(880	)	$	2,011
Long-term portion (included in Deposits and other assets)	625		—		—			—			625
Subtotal	$	2,163	$	1,353	$	—		$	(880	)	$	2,636
	$	404,063	$	1,884	$	(130	)	$	(880	)	$	404,937

Schedule of investments temporarily impaired

		Less than 12 months of temporary impairment
	Number of Investments	Estimated Fair Value		Unrealized Losses
Corporate debt securities	59	$	118,695	$	(586	)
Debt securities issued by U.S. government agencies	10	33,685		(72		)
Debt securities issued by states of the United States and political subdivisions of the states	5	9,685		(26		)
Total temporarily impaired securities	74	$	162,065	$	(684	)