Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 505,883	$ 364,930
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	1,501,845	1,397,905
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	3,279	3,678
Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	1,352	1,562
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	235,431	261,962
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	270,452	102,968
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	7,423	3,588
Cash and Cash Equivalents [Member] \| Corporate Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	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	735,491	695,809
Available-for-sale Securities [Member] \| Corporate Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	1,352	1,562
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	540,954	530,522
Available-for-sale Securities [Member] \| Agency Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Municipal securities [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Municipal securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	3,910	14,878
Available-for-sale Securities [Member] \| Municipal securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
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	210,231	152,045
Available-for-sale Securities [Member] \| Government securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Accrued Expenses and Other Current Liabilities [Member] \| Level 1 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Accrued Expenses and Other Current Liabilities [Member] \| Level 2 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	3,279	3,678
Accrued Expenses and Other Current Liabilities [Member] \| Level 3 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	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	3,836	1,063
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
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	2,009,080	1,764,397
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	3,279	3,678
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	235,431	261,962
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	270,452	102,968
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	7,423	3,588
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	736,843	697,371
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	540,954	530,522
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Municipal securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	3,910	14,878
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	210,231	152,045
Estimate of Fair Value Measurement [Member] \| Accrued Expenses and Other Current Liabilities [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	3,279	3,678
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	$ 3,836	$ 1,063

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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

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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://www.xbrl.org/2003/role/presentationRef
-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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=51814546&loc=SL51823488-111719

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- 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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- 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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 1
-Subparagraph a, f, g
-Article 7

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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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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