Fair Value Of Financial Instruments (Fair Value, Assets And Liabilities Measured On Recurring Basis) (Details) - Measured On A Recurring Basis [Member] - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	$ 1,877,802	$ 1,824,595
Total fair of value of liabilities	22,676	30,290
Embedded Derivative Financial Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	22,611	30,126
Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	141,209	137,593
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	1,733,258	1,685,882
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	2,772	890
Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts assets	563	230
Foreign currency forward contracts liabilities	65	164
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	1,877,239	1,824,365
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	141,209	137,593
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	1,733,258	1,685,882
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	2,772	890
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	563	230
Total fair of value of liabilities	65	164
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	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	563	230
Foreign currency forward contracts liabilities	65	164
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	22,611	30,126
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	22,611	30,126
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] | 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