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Derivative Financial Instruments - Additional Information (Details) - Dec. 31, 2018 £ in Millions, $ in Millions	USD ($) derivative $ / unit	GBP (£) derivative $ / unit
Derivative [Line Items]
Number of contracts with a contingent feature in a net liability position | derivative	0	0
Forward contracts
Derivative [Line Items]
Derivative, number of contracts | derivative	2	2
Cash collateral held from counterparty | $	$ 3.1
Cash collateral held at counterparty | $	$ 28.0
Collar contracts
Derivative [Line Items]
Derivative, number of contracts | derivative	2	2
Designated as Hedging Instrument | Net Investment Hedging | Forward contract expiring 2024
Derivative [Line Items]
Derivative, notional amount	$ 400.0	£ 285.8
Designated as Hedging Instrument | Net Investment Hedging | Forward contract expiring 2021
Derivative [Line Items]
Derivative, notional amount	$ 450.0	£ 325.3
Designated as Hedging Instrument | Net Investment Hedging | Collar contract-call option | Minimum
Derivative [Line Items]
Derivative, option strike price (in dollars per unit)	1.288	1.288
Designated as Hedging Instrument | Net Investment Hedging | Collar contract-call option | Maximum
Derivative [Line Items]
Derivative, option strike price (in dollars per unit)	1.535	1.535
Designated as Hedging Instrument | Net Investment Hedging | Collar contract-put option | Minimum
Derivative [Line Items]
Derivative, option strike price (in dollars per unit)	1.318	1.318
Designated as Hedging Instrument | Net Investment Hedging | Collar contract-put option | Maximum
Derivative [Line Items]
Derivative, option strike price (in dollars per unit)	1.448	1.448

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- Definition

Derivative, Net Liability Position, Number of Instruments

+ References

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- Definition

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

+ References

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

Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959

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-Section 50
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-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
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- Definition

The strike price on the foreign currency option contract such as a put option or a call option.

+ References

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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.

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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