Fair Value Of Financial Instruments (Fair Value, Assets And Liabilities Measured On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Total Fair Value [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	$ 366,219		$ 165,054
Total fair of value of liabilities	12,810		12,069
Total Fair Value [Member] | Measured On A Recurring Basis [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	333,165		132,145
Total Fair Value [Member] | Measured On A Recurring Basis [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 in fixed income securities	32,803		32,860
Total Fair Value [Member] | Measured On A Recurring Basis [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	251		49
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	333,165		132,145
Total fair of value of liabilities	0		0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Measured On A Recurring Basis [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments in money market funds	333,165		132,145
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Measured On A Recurring Basis [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 in fixed income securities	0		0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Measured On A Recurring Basis [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	0		0
Significant Other Observable Inputs (Level 2) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total fair value of assets	33,054		32,909
Total fair of value of liabilities	372		444
Significant Other Observable Inputs (Level 2) [Member] | Measured On A Recurring Basis [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] | Measured On A Recurring Basis [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 in fixed income securities	32,803		32,860
Significant Other Observable Inputs (Level 2) [Member] | Measured On A Recurring Basis [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	251		49
Significant Unobservable Inputs (Level 3) [Member] | Measured On A Recurring Basis [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	12,438		11,625
Significant Unobservable Inputs (Level 3) [Member] | Measured On A Recurring Basis [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] | Measured On A Recurring Basis [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 in fixed income securities	0
Significant Unobservable Inputs (Level 3) [Member] | Measured On A Recurring Basis [Member] | Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	0
Forward Contracts [Member] | Total Fair Value [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	372		444
Forward Contracts [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	0		0
Forward Contracts [Member] | Significant Other Observable Inputs (Level 2) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	372		444
Forward Contracts [Member] | Significant Unobservable Inputs (Level 3) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency forward contracts	0		0
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	12,438	10,950	11,625	10,500
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	813	450
Derivative Financial Instruments, Liabilities [Member] | Total Fair Value [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	12,438		11,625
Derivative Financial Instruments, Liabilities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	0		0
Derivative Financial Instruments, Liabilities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	0		0
Derivative Financial Instruments, Liabilities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Measured On A Recurring Basis [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	$ 12,438		$ 11,625