Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 843,245	$ 753,402
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	1,560,872	1,791,266
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	989	4,435
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	394	998
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	0	0
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Cash [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	753,839	528,637
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Cash [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Cash [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	89,406	224,765
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	1,526	82,693
Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	804,088	839,968
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	394	998
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Agency Securities [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Agency Securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	478,767	411,493
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Agency Securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Municipal securities [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Municipal securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	3,977	9,988
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Municipal securities [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Government securities [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Government securities [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	269,250	444,618
Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Government 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] \| Fair Value, Measurements, Recurring [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] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	3,264	2,506
Foreign Exchange Contract [Member] \| Prepaid Expenses and Other Current Assets [Member] \| Fair Value, Measurements, Recurring [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] \| Fair Value, Measurements, Recurring [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] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	989	4,435
Foreign Exchange Contract [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Measurements, Recurring [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets	2,404,511	2,545,666
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities	989	4,435
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Cash [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	753,839	528,637
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	89,406	224,765
Estimate of Fair Value Measurement [Member] \| Cash and Cash Equivalents [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	1,526	82,693
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	804,482	840,966
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Agency Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	478,767	411,493
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Municipal securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	3,977	9,988
Estimate of Fair Value Measurement [Member] \| Available-for-sale Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Government securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities	269,250	444,618
Estimate of Fair Value Measurement [Member] \| Foreign Exchange Contract [Member] \| Prepaid Expenses and Other Current Assets [Member] \| Fair Value, Measurements, Recurring [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	3,264	2,506
Estimate of Fair Value Measurement [Member] \| Foreign Exchange Contract [Member] \| Accrued Expenses and Other Current Liabilities [Member] \| Fair Value, Measurements, Recurring [Member]
Liabilities, Fair Value Disclosure [Abstract]
Foreign currency derivatives	989	4,435
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Foreign Exchange Contract [Member] \| Prepaid Expenses and Other Current Assets [Member]
Assets, Fair Value Disclosure [Abstract]
Prepaid expenses and other current assets	$ 2,791	$ 460

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=66048111&loc=d3e19207-110258

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- References

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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://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=84234895&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=82849420&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=82924980&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
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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=82895926&loc=d3e24584-111560

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: 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=75030427&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

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