Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 556,484	$ 516,775
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	383,553	89,570
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	6,069	1,390
Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	500	1,000
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Cash and Cash Equivalents [Member] | Cash [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	548,220	474,756
Cash and Cash Equivalents [Member] | Cash [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Cash [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	8,264	42,019
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	2,342	8,993
Cash and Cash Equivalents [Member] | Corporate Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] | Government securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0
Cash and Cash Equivalents [Member] | Government securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	9,998
Cash and Cash Equivalents [Member] | Government securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0
Cash and Cash Equivalents [Member] | Agency Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents		0
Cash and Cash Equivalents [Member] | Agency Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents		19,993
Cash and Cash Equivalents [Member] | Agency Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents		0
Available-for-sale Securities [Member] | Corporate Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Corporate Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	196,584	47,884
Available-for-sale Securities [Member] | Corporate Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	500	1,000
Available-for-sale Securities [Member] | Government securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Government securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	132,469	9,129
Available-for-sale Securities [Member] | Government securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Agency Securities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] | Agency Securities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	39,995	1,682
Available-for-sale Securities [Member] | Agency Securities [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Foreign Exchange Contract [Member] | Prepaid Expenses and Other Current Assets [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	0	0
Foreign Exchange Contract [Member] | Prepaid Expenses and Other Current Assets [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	2,165	1,889
Foreign Exchange Contract [Member] | Prepaid Expenses and Other Current Assets [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	0	0
Foreign Exchange Contract [Member] | Accrued Expenses and Other Current Liabilities [Member] | Level 1 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Foreign Exchange Contract [Member] | Accrued Expenses and Other Current Liabilities [Member] | Level 2 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	6,069	1,390
Foreign Exchange Contract [Member] | Accrued Expenses and Other Current Liabilities [Member] | Level 3 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	940,537	607,345
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	6,069	1,390
Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member] | Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	548,220	474,756
Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	8,264	42,019
Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member] | Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	2,342	8,993
Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member] | Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	9,998
Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member] | Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents		19,993
Estimate of Fair Value Measurement [Member] | Available-for-sale Securities [Member] | Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	197,084	48,884
Estimate of Fair Value Measurement [Member] | Available-for-sale Securities [Member] | Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	132,469	9,129
Estimate of Fair Value Measurement [Member] | Available-for-sale Securities [Member] | Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	39,995	1,682
Estimate of Fair Value Measurement [Member] | Foreign Exchange Contract [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	2,165	1,889
Estimate of Fair Value Measurement [Member] | Foreign Exchange Contract [Member] | Accrued Expenses and Other Current Liabilities [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	$ 6,069	$ 1,390