Fair Value Of Financial Instruments (Fair Value, Assets And Liabilities Measured On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	$ 3,105
Measured On A Recurring Basis [Member] | Total Fair Value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	1,517,413	1,493,824
Total fair of value of liabilities	17,802	11,968
Measured On A Recurring Basis [Member] | Total Fair Value [Member] | Embedded Derivative Financial Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	17,636	11,203
Measured On A Recurring Basis [Member] | Total Fair Value [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	14,219	38,054
Measured On A Recurring Basis [Member] | Total Fair Value [Member] | Debt Securities Issued By The U.S. Treasury And Other U.S. Government Corporations And Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	1,499,722	1,452,358
Measured On A Recurring Basis [Member] | Total Fair Value [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	3,105	3,341
Measured On A Recurring Basis [Member] | Total Fair Value [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts assets	367	71
Foreign currency forward contracts liabilities	166	765
Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	1,483,907	1,457,334
Total fair of value of liabilities	0	0
Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Embedded Derivative Financial Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	0	0
Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	14,219	38,054
Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Debt Securities Issued By The U.S. Treasury And Other U.S. Government Corporations And Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	1,466,583	1,419,280
Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	3,105	0
Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts assets	0	0
Foreign currency forward contracts liabilities	0	0
Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	33,506	36,490
Total fair of value of liabilities	166	765
Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Embedded Derivative Financial Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	0	0
Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	0	0
Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities Issued By The U.S. Treasury And Other U.S. Government Corporations And Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	33,139	33,078
Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	0	3,341
Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts assets	367	71
Foreign currency forward contracts liabilities	166	765
Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	0	0
Total fair of value of liabilities	17,636	11,203
Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Embedded Derivative Financial Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	17,636	11,203
Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	0	0
Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities Issued By The U.S. Treasury And Other U.S. Government Corporations And Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	0	0
Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	0	0
Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts assets	0	0
Foreign currency forward contracts liabilities	$ 0	$ 0