Fair Value Measurements (Schedule Of Fair Values Of Financial Instruments Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Total assets measured at fair value	$ 383,879	$ 418,334
Contingent consideration	8,122	37,887
Total liabilities measured at fair value	8,122	37,887
Money Market Funds [Member]
Money market and other funds	383,236	395,664
Corporate Debt Securities [Member]
Corporate debt securities	643	22,670
Level 1 [Member]
Total assets measured at fair value	383,236	395,664
Contingent consideration	0	0
Total liabilities measured at fair value	0	0
Level 1 [Member] | Money Market Funds [Member]
Money market and other funds	383,236	395,664
Level 1 [Member] | Corporate Debt Securities [Member]
Corporate debt securities	0	0
Level 2 [Member]
Total assets measured at fair value	643	623
Contingent consideration	0	0
Total liabilities measured at fair value	0	0
Level 2 [Member] | Money Market Funds [Member]
Money market and other funds	0	0
Level 2 [Member] | Corporate Debt Securities [Member]
Corporate debt securities	643	623
Level 3 [Member]
Total assets measured at fair value	0	22,047
Contingent consideration	8,122	37,887
Total liabilities measured at fair value	8,122	37,887
Level 3 [Member] | Money Market Funds [Member]
Money market and other funds	0	0
Level 3 [Member] | Corporate Debt Securities [Member]
Corporate debt securities	$ 0	$ 22,047