Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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Derivatives and Hedge Accounting - Additional Information (Details) £ in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 GBP (£)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 GBP (£)
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gains which could be reclassified into earnings within the next 12 months	$ (6,158)
Maximum outstanding term of cash flow hedges	45 months
Derivatives Designated as Hedging Instruments \| Derivatives in Cash Flow Hedging Relationships \| Foreign currency exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange contracts outstanding	$ 364,395		$ 300,757
Derivatives not Designated as Hedging Instruments \| Foreign currency exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange contracts outstanding	$ 140,055	£ 18,044	$ 98,967	£ 17,947