Investments and Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 476,038	$ 398,963
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	47,837	495,922
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	1,101	1,447
Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	500	500
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	401,653	375,874
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	74,385	23,089
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	1,705	166,436
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		187,496
Cash and Cash Equivalents [Member] \| Government 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	26,798	70,184
Available-for-sale Securities [Member] \| Corporate Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	500	500
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	5,000	64,494
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
Available-for-sale Securities [Member] \| Agency Securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		3,300
Available-for-sale Securities [Member] \| Agency Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		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	14,334	4,012
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	1,101	1,447
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	524,375	895,385
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	1,101	1,447
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	401,653	375,874
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	74,385	23,089
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	1,705	166,436
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents		187,496
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	27,298	70,684
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	5,000	64,494
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		3,300
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	14,334	4,012
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	$ 1,101	$ 1,447

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- References

No definition available.

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624163-113959

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of liability contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward (delivery or nondelivery) contracts, and swaps entered into.

+ References

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of financial and nonfinancial obligations.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

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Balance Type:	na
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