Investments and Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 396,655	$ 398,963
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Level 1 [Member] \| Cash and Cash Equivalents [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	291,396	375,874
Level 1 [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	105,259	23,089
Level 1 [Member] \| Cash and Cash Equivalents [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 1 [Member] \| Cash and Cash Equivalents [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 1 [Member] \| Available-for-sale Securities [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Level 1 [Member] \| Available-for-sale Securities [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		0
Level 1 [Member] \| Available-for-sale Securities [Member] \| Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		0
Level 1 [Member] \| Prepaid Expenses and Other Current Assets [Member] \| Foreign Exchange Contract [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	0	0
Level 1 [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Foreign Exchange Contract [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	78,913	495,922
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	1,469	1,447
Level 2 [Member] \| Cash and Cash Equivalents [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 2 [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 2 [Member] \| Cash and Cash Equivalents [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	11,016	166,436
Level 2 [Member] \| Cash and Cash Equivalents [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	20,898	187,496
Level 2 [Member] \| Available-for-sale Securities [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	34,924	70,184
Level 2 [Member] \| Available-for-sale Securities [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		64,494
Level 2 [Member] \| Available-for-sale Securities [Member] \| Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		3,300
Level 2 [Member] \| Prepaid Expenses and Other Current Assets [Member] \| Foreign Exchange Contract [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	12,075	4,012
Level 2 [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Foreign Exchange Contract [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	1,469	1,447
Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	500	500
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Level 3 [Member] \| Cash and Cash Equivalents [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 3 [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 3 [Member] \| Cash and Cash Equivalents [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 3 [Member] \| Cash and Cash Equivalents [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Level 3 [Member] \| Available-for-sale Securities [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	500	500
Level 3 [Member] \| Available-for-sale Securities [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		0
Level 3 [Member] \| Available-for-sale Securities [Member] \| Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities		0
Level 3 [Member] \| Prepaid Expenses and Other Current Assets [Member] \| Foreign Exchange Contract [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	0	0
Level 3 [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Foreign Exchange Contract [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	476,068	895,385
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	1,469	1,447
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	291,396	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	105,259	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	11,016	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	20,898	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	35,424	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		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] \| Prepaid Expenses and Other Current Assets [Member] \| Foreign Exchange Contract [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	12,075	4,012
Estimate of Fair Value Measurement [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Foreign Exchange Contract [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	$ 1,469	$ 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=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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://www.xbrl.org/2003/role/disclosureRef
-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 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

Reference 3: 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 4: 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 5: 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=125515794&loc=SL5624163-113959

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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.

+ Details

Name:	us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure
Namespace Prefix:	us-gaap_
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=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_InvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration