Investments (Maturities Of Marketable Securities And Restricted Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Marketable Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Less than one year, Amortized Cost	$ 117,846
Total Amortized Cost	117,846
Less than one year, Fair Value	119,234
Total Fair Value	119,234
Marketable Securities, Non-Current [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Due in year two through year three, Amortized Cost	219,106
Due in year four through year five, Amortized Cost	41,695
Due after five years, Amortized Cost	16,193
Total Amortized Cost	276,994
Due in year two through year three, Fair Value	221,040
Due in year four through year five, Fair Value	42,473
Due after five years, Fair Value	16,445
Total Fair Value	279,958
Restricted Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Less than one year, Amortized Cost	34,914
Due in year two through year three, Amortized Cost	41,663
Due in year four through year five, Amortized Cost	3,295
Due after five years, Amortized Cost	131
Total Amortized Cost	80,003
Less than one year, Fair Value	35,003
Due in year two through year three, Fair Value	41,813
Due in year four through year five, Fair Value	3,245
Due after five years, Fair Value	132
Total Fair Value	$ 80,193