Fair Value (Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Total assets	$ 244,601	$ 90,495
Liabilities:
Acquisition-related contingent consideration	180,111	185,157
Total liabilities	180,111	185,157
Money Market Funds [Member]
Assets:
Total assets	85,286	14,502
Repurchase Agreements [Member]
Assets:
Total assets		10,000
Commercial Paper [Member]
Assets:
Total assets	42,373	13,755
U.S. Government Agencies and Securities [Member]
Assets:
Total assets	46,202	8,539
Corporate Bonds [Member]
Assets:
Total assets	48,140	24,852
Asset-backed Securities [Member]
Assets:
Total assets	22,600	18,847
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total assets	46,202	8,539
Liabilities:
Acquisition-related contingent consideration
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Government Agencies and Securities [Member]
Assets:
Total assets	46,202	8,539
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets	198,399	81,956
Liabilities:
Acquisition-related contingent consideration
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Assets:
Total assets	85,286	14,502
Significant Other Observable Inputs (Level 2) [Member] | Repurchase Agreements [Member]
Assets:
Total assets		10,000
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
Assets:
Total assets	42,373	13,755
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Assets:
Total assets	48,140	24,852
Significant Other Observable Inputs (Level 2) [Member] | Asset-backed Securities [Member]
Assets:
Total assets	22,600	18,847
Significant Other Unobservable Inputs (Level 3) [Member]
Liabilities:
Acquisition-related contingent consideration	180,111	185,157
Total liabilities	$ 180,111	$ 185,157