Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	$ 19,459	$ 25,709
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	19,459	25,709
Estimated Fair Value Recurring [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	19,459	25,709
Estimated Fair Value Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	245,389	159,719
Estimated Fair Value Recurring [Member] | Level 1 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	0	0
Estimated Fair Value Recurring [Member] | Level 1 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	245,389	159,719
Estimated Fair Value Recurring [Member] | Level 2 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	19,459	25,709
Estimated Fair Value Recurring [Member] | Level 2 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	0	0
Estimated Fair Value Recurring [Member] | Level 3 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	0	0
Estimated Fair Value Recurring [Member] | Level 3 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets and liabilities measured at fair value	$ 0	$ 0