Fair Value Measurements (Fair Values of Financial Instruments Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value	$ 317,760	$ 418,334
Contingent consideration	8,352	37,887
Total liabilities measured at fair value	8,352	37,887
Money market and other funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market and other funds	317,107	395,664
Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate debt securities	653	22,670
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value	317,107	395,664
Contingent consideration	0	0
Total liabilities measured at fair value	0	0
Level 1 | Money market and other funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market and other funds	317,107	395,664
Level 1 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate debt securities	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value	653	623
Contingent consideration	0	0
Total liabilities measured at fair value	0	0
Level 2 | Money market and other funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market and other funds	0	0
Level 2 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate debt securities	653	623
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value	0	22,047
Contingent consideration	8,352	37,887
Total liabilities measured at fair value	8,352	37,887
Level 3 | Money market and other funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market and other funds	0	0
Level 3 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate debt securities	$ 0	$ 22,047