Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011	Dec. 31, 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 639,130		$ 563,275		$ 606,377	$ 341,683
Short-term investments	229,975		246,273
Long-term investments	50,333		45,138
Long term investment maturities - begin	14 months from March 31, 2012
Long term investment maturities - end	24 months from March 31, 2012
Fair Value | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	639,130		563,275
Fair Value | Level 1 | Public debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	1,022,534	[1]	1,043,549	[1]
Fair Value | Level 2 | Non public debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	534,805	[1]	543,309	[1]
Fair Value | Certificates Of Deposit | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	27,195	[2],[3]	27,444	[2],[3]
Fair Value | Government Backed Securities | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	202,780	[2],[3],[4]	218,829	[2],[3],[4]
Long-term investments	50,429	[3],[4],[5]	45,310	[3],[4],[5]
Book Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	639,130		563,275
Book Value | Public debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	983,250	[1]	983,250	[1]
Book Value | Non public debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	542,477	[1]	542,398	[1]
Book Value | Certificates Of Deposit
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	27,195	[2],[3]	27,444	[2],[3]
Book Value | Government Backed Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	202,780	[2],[3],[4]	218,829	[2],[3],[4]
Long-term investments	$ 50,333	[3],[4],[5]	$ 45,138	[3],[4],[5]

[1] Excludes capital lease obligations and current portion of Long-term debt.

[2] Maturities are less than twelve months from the respective balance sheet dates.

[3] Designated as held-to-maturity investments and recorded at amortized cost in the Consolidated Balance Sheet.

[4] Includes U.S. treasuries and corporate notes guaranteed under the Federal Deposit Insurance Corporation’s Temporary Liquidity Guarantee Program.

[5] At March 31, 2012, maturities range between 14 and 24 months.