Fair Value Disclosures (Cash, Cash Equivalents And Investments, As Well As The Hierarchy For Financial Instruments Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 180,147		$ 70,136	$ 94,885	$ 107,717
Classified As Cash Equivalents [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	49,994	[1]
Classified As Cash Equivalents [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	49,994	[1]
Money Market Funds [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	45,396		44,044
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	45,396		44,044
US Treasury Bills [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	199,939		74,996
US Treasury Bills [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 199,939		$ 74,996

[1] Includes a $50.0 million U.S. Treasury bill maturing within ninety days of March 31, 2012 and classified as a cash equivalent on the consolidated balance sheet.