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Subsequent Events (Details) $ in Millions	Oct. 31, 2018 USD ($) $ / unit	Oct. 31, 2018 GBP (£) $ / unit	Sep. 30, 2018 USD ($)	Sep. 30, 2018 GBP (£)	Aug. 28, 2018 $ / unit
Designated as Hedging Instrument | Forward contracts | Net Investment Hedging
Subsequent Event [Line Items]
Derivative notional amount			$ 400.0	£ 285,800,000
Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Minimum
Subsequent Event [Line Items]
Derivative, option strike price (in dollars per unit)					1.288
Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Maximum
Subsequent Event [Line Items]
Derivative, option strike price (in dollars per unit)					1.535
Unsecured Debt | Term Loan
Subsequent Event [Line Items]
Principal amount at maturity | £				290,000,000
Additional borrowing amount | £				£ 50,000,000.0
Subsequent Event | Designated as Hedging Instrument | Forward contracts | Net Investment Hedging
Subsequent Event [Line Items]
Derivative notional amount	$ 450.0	£ 325,300,000
Subsequent Event | Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Minimum
Subsequent Event [Line Items]
Derivative, option strike price (in dollars per unit)	1.318	1.318
Subsequent Event | Designated as Hedging Instrument | Forward contracts | Net Investment Hedging | Maximum
Subsequent Event [Line Items]
Derivative, option strike price (in dollars per unit)	1.448	1.448
Subsequent Event | Unsecured Debt | Term Loan
Subsequent Event [Line Items]
Principal amount at maturity | $	$ 450.0
Additional borrowing amount | $	$ 75.0

X

- Definition

Line of Credit Facility, Maximum Borrowing Capacity, Additional Amount

+ References

No definition available.

+ Details

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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

+ Details

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

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- Definition

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+ References

No definition available.

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X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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