Balance Sheet Information (Details) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Total available-for-sale securities
Amortized Cost	$ 212,538,000		$ 212,538,000		$ 394,083,000
Gains in Accumulated Other Comprehensive Income	189,000		189,000		97,000
Estimated Fair Value	212,727,000		212,727,000		394,180,000
Total proceeds from sale of available-for-sale securities	292,900,000	11,000,000	667,216,000	11,013,000
Gross realized gains	200,000		400,000
Net unrealized (losses) gain on available-for-sale securities	(100,000)	200,000	100,000	200,000
Estimated fair value of contractual maturities of available-for-sale debt securities
Due in one year or less	31,503,000		31,503,000
Due in 1-2 years	181,224,000		181,224,000
Total investments in debt securities	212,727,000		212,727,000		394,180,000
Commercial paper
Total available-for-sale securities
Amortized Cost	24,284,000		24,284,000		128,527,000
Gains in Accumulated Other Comprehensive Income	6,000		6,000		61,000
Estimated Fair Value	24,290,000		24,290,000		128,588,000
Estimated fair value of contractual maturities of available-for-sale debt securities
Total investments in debt securities	24,290,000		24,290,000		128,588,000
FDIC insured corporate bonds
Total available-for-sale securities
Amortized Cost	137,138,000		137,138,000		129,353,000
Gains in Accumulated Other Comprehensive Income	153,000		153,000		24,000
Estimated Fair Value	137,291,000		137,291,000		129,377,000
Estimated fair value of contractual maturities of available-for-sale debt securities
Total investments in debt securities	137,291,000		137,291,000		129,377,000
Treasury bills
Total available-for-sale securities
Amortized Cost	51,116,000		51,116,000		136,203,000
Gains in Accumulated Other Comprehensive Income	30,000		30,000		12,000
Estimated Fair Value	51,146,000		51,146,000		136,215,000
Estimated fair value of contractual maturities of available-for-sale debt securities
Total investments in debt securities	$ 51,146,000		$ 51,146,000		$ 136,215,000

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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