Fair Value Measurements (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial instruments carried at fair value (asset positions):
Total financial assets	$ 2,278,590	$ 1,836,605
Financial instruments carried at fair value (liability positions):
Total financial liabilities	(968)	(448)
Level 1
Financial instruments carried at fair value (asset positions):
Total financial assets	1,853,870	1,410,155
Financial instruments carried at fair value (liability positions):
Total financial liabilities	0	0
Level 2
Financial instruments carried at fair value (asset positions):
Total financial assets	424,720	426,450
Financial instruments carried at fair value (liability positions):
Total financial liabilities	(968)	(448)
Level 3
Financial instruments carried at fair value (asset positions):
Total financial assets	0	0
Financial instruments carried at fair value (liability positions):
Total financial liabilities	0	0
Prepaid expenses and other current assets \| Foreign currency forward contracts
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	13,215	19,023
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Level 1
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	0	0
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Level 2
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	13,215	19,023
Prepaid expenses and other current assets \| Foreign currency forward contracts \| Level 3
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	0	0
Other assets \| Foreign currency forward contracts
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	314
Total financial assets		1,514
Other assets \| Foreign currency forward contracts \| Level 1
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	0
Total financial assets		0
Other assets \| Foreign currency forward contracts \| Level 2
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	314
Total financial assets		1,514
Other assets \| Foreign currency forward contracts \| Level 3
Financial instruments carried at fair value (asset positions):
Foreign currency forward contracts	0
Total financial assets		0
Other current liabilities \| Foreign currency forward contracts
Financial instruments carried at fair value (liability positions):
Derivative liability current	(761)	(340)
Other current liabilities \| Foreign currency forward contracts \| Level 1
Financial instruments carried at fair value (liability positions):
Derivative liability current	0	0
Other current liabilities \| Foreign currency forward contracts \| Level 2
Financial instruments carried at fair value (liability positions):
Derivative liability current	(761)	(340)
Other current liabilities \| Foreign currency forward contracts \| Level 3
Financial instruments carried at fair value (liability positions):
Derivative liability current	0	0
Other long-term liabilities \| Foreign currency forward contracts
Financial instruments carried at fair value (liability positions):
Derivative liability, noncurrent	(207)	(108)
Other long-term liabilities \| Foreign currency forward contracts \| Level 1
Financial instruments carried at fair value (liability positions):
Derivative liability, noncurrent	0	0
Other long-term liabilities \| Foreign currency forward contracts \| Level 2
Financial instruments carried at fair value (liability positions):
Derivative liability, noncurrent	(207)	(108)
Other long-term liabilities \| Foreign currency forward contracts \| Level 3
Financial instruments carried at fair value (liability positions):
Derivative liability, noncurrent	0	0
Money market funds
Financial instruments carried at fair value (asset positions):
Cash equivalents	1,561,770	1,226,603
Money market funds \| Level 1
Financial instruments carried at fair value (asset positions):
Cash equivalents	1,561,770	1,226,603
Money market funds \| Level 2
Financial instruments carried at fair value (asset positions):
Cash equivalents	0	0
Money market funds \| Level 3
Financial instruments carried at fair value (asset positions):
Cash equivalents	0	0
Government-sponsored enterprise securities
Financial instruments carried at fair value (asset positions):
Cash equivalents	24,519	7,123
Marketable securities	8,247	10,704
Government-sponsored enterprise securities \| Level 1
Financial instruments carried at fair value (asset positions):
Cash equivalents	24,519	7,123
Marketable securities	8,247	10,704
Government-sponsored enterprise securities \| Level 2
Financial instruments carried at fair value (asset positions):
Cash equivalents	0	0
Marketable securities	0	0
Government-sponsored enterprise securities \| Level 3
Financial instruments carried at fair value (asset positions):
Cash equivalents	0	0
Marketable securities	0	0
Commercial paper
Financial instruments carried at fair value (asset positions):
Cash equivalents	22,234	58,268
Marketable securities	125,572	100,390
Commercial paper \| Level 1
Financial instruments carried at fair value (asset positions):
Cash equivalents	0	0
Marketable securities	0	0
Commercial paper \| Level 2
Financial instruments carried at fair value (asset positions):
Cash equivalents	22,234	58,268
Marketable securities	125,572	100,390
Commercial paper \| Level 3
Financial instruments carried at fair value (asset positions):
Cash equivalents	0	0
Marketable securities	0	0
U.S. Treasury securities
Financial instruments carried at fair value (asset positions):
Cash equivalents		5,966
Marketable securities	5,892	6,026
U.S. Treasury securities \| Level 1
Financial instruments carried at fair value (asset positions):
Cash equivalents		5,966
Marketable securities	5,892	6,026
U.S. Treasury securities \| Level 2
Financial instruments carried at fair value (asset positions):
Cash equivalents		0
Marketable securities	0	0
U.S. Treasury securities \| Level 3
Financial instruments carried at fair value (asset positions):
Cash equivalents		0
Marketable securities	0	0
Corporate debt securities
Financial instruments carried at fair value (asset positions):
Marketable securities	249,426	233,665
Corporate debt securities \| Level 1
Financial instruments carried at fair value (asset positions):
Marketable securities	0	0
Corporate debt securities \| Level 2
Financial instruments carried at fair value (asset positions):
Marketable securities	249,426	233,665
Corporate debt securities \| Level 3
Financial instruments carried at fair value (asset positions):
Marketable securities	0	0
Corporate equity securities
Financial instruments carried at fair value (asset positions):
Marketable securities	267,401	167,323
Corporate equity securities \| Level 1
Financial instruments carried at fair value (asset positions):
Marketable securities	253,442	153,733
Corporate equity securities \| Level 2
Financial instruments carried at fair value (asset positions):
Marketable securities	13,959	13,590
Corporate equity securities \| Level 3
Financial instruments carried at fair value (asset positions):
Marketable securities	$ 0	$ 0

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=99377789&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, after the effects of master netting arrangements, of a financial liability or 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, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or 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, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

+ Details

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

- Definition

Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

+ References

No definition available.

+ Details

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

- Definition

Fair value as of the balance sheet date of all foreign currency derivatives designated as cash flow hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(b),(c)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

+ Details

Name:	us-gaap_ForeignCurrencyCashFlowHedgeDerivativeAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

- Definition

Amount of investment in marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_OtherCurrentLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_OtherNoncurrentLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: