Fair Value Of Financial Instruments (Fair Value, Assets And Liabilities Measured On Recurring Basis) (Details) - Measured On A Recurring Basis [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Total Fair Value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	$ 1,826,594	$ 1,318,859
Total fair of value of liabilities	25,187	26,924
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	25,054	26,755
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	113,223	85,453
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	1,712,986	1,233,076
Total Fair Value [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	101
Total Fair Value [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts assets	284	330
Foreign currency forward contracts liabilities	133	169
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	1,826,310	1,318,529
Total fair of value of liabilities	0	0
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
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	113,223	85,453
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	1,712,986	1,233,076
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	101
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
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	284	330
Total fair of value of liabilities	133	169
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
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
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	0	0
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
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	284	330
Foreign currency forward contracts liabilities	133	169
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	25,054	26,755
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	25,054	26,755
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
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
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
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