Fair Value Measurements (Schedule Of Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	$ 285,085	$ 236,949
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	139,631	130,771
Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	60,473	40,400
Commercial Paper - Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	24,234	20,228
Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	22,481	27,315
U.S. Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	16,286	12,231
Treasury Bills [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	10,993
Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities		1,400
Measured At Fair Value On Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	285,085	236,949
Measured At Fair Value On Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	285,085	236,949
Measured At Fair Value On Recurring Basis [Member] | Equity Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	2,119	2,182
Measured At Fair Value On Recurring Basis [Member] | Equity Mutual Funds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	2,119	2,182
Measured At Fair Value On Recurring Basis [Member] | Foreign Currency Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	971	8,926
Fair value of Liabilities	7,004	1,081
Measured At Fair Value On Recurring Basis [Member] | Foreign Currency Exchange Contracts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	971	8,926
Fair value of Liabilities	7,004	1,081
Measured At Fair Value On Recurring Basis [Member] | Deferred Compensation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Liabilities	2,119	2,182
Measured At Fair Value On Recurring Basis [Member] | Deferred Compensation [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Liabilities	2,119	2,182
Measured At Fair Value On Recurring Basis [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	20,924	34,208
Measured At Fair Value On Recurring Basis [Member] | Money Market Funds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	20,924	34,208
Measured At Fair Value On Recurring Basis [Member] | Certificates Of Deposit - Maturity Less Than 90 Days [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets		1,500
Measured At Fair Value On Recurring Basis [Member] | Certificates Of Deposit - Maturity Less Than 90 Days [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets		1,500
Measured At Fair Value On Recurring Basis [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	3,089	898
Measured At Fair Value On Recurring Basis [Member] | Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	3,089	898
Measured At Fair Value On Recurring Basis [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	2,500
Total marketable securities	139,631	130,771
Measured At Fair Value On Recurring Basis [Member] | Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	2,500
Total marketable securities	139,631	130,771
Measured At Fair Value On Recurring Basis [Member] | Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	750
Total marketable securities	60,473	40,400
Measured At Fair Value On Recurring Basis [Member] | Certificates Of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Assets	750
Total marketable securities	60,473	40,400
Measured At Fair Value On Recurring Basis [Member] | Commercial Paper - Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	24,234	20,228
Measured At Fair Value On Recurring Basis [Member] | Commercial Paper - Marketable Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	24,234	20,228
Measured At Fair Value On Recurring Basis [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	22,481	27,315
Measured At Fair Value On Recurring Basis [Member] | Asset-backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	22,481	27,315
Measured At Fair Value On Recurring Basis [Member] | U.S. Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	16,286	12,231
Measured At Fair Value On Recurring Basis [Member] | U.S. Government Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	16,286	12,231
Measured At Fair Value On Recurring Basis [Member] | Treasury Bills [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	10,993
Measured At Fair Value On Recurring Basis [Member] | Treasury Bills [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	10,993
Measured At Fair Value On Recurring Basis [Member] | Agency Bonds- Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	10,987	4,604
Measured At Fair Value On Recurring Basis [Member] | Agency Bonds- Marketable Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	$ 10,987	4,604
Measured At Fair Value On Recurring Basis [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities		1,400
Measured At Fair Value On Recurring Basis [Member] | Municipal Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities		$ 1,400