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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
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-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

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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

Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

+ References

No definition available.

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- Definition

Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580

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-Paragraph 10A
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-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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Fair Value of Financial Instruments - Derivatives (Details) € in Millions, £ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 GBP (£) contract	Dec. 31, 2018 GBP (£) contract	Dec. 31, 2018 EUR (€) contract	Sep. 30, 2018 contract	Dec. 31, 2017 USD ($) contract
Derivatives, Fair Value [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax \| $	$ 200,000	$ 200,000	$ 400,000	$ 400,000
Foreign currency contract, asset, fair value disclosure \| $									$ 0
Forward Contracts
Derivatives, Fair Value [Line Items]
Derivative, number of instruments held \| contract						2	2	5	2
Derivative, notional amount						£ 4.1	€ 12.9
Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, number of instruments held \| contract					26
Not Designated as Hedging Instrument [Member] \| Foreign Currency Contract, Euro [Member]
Derivatives, Fair Value [Line Items]
Derivative, notional amount					£ 10.0	16.0
Not Designated as Hedging Instrument [Member] \| Foreign Currency Contract, Pound [Member]
Derivatives, Fair Value [Line Items]
Derivative, notional amount					4.0	£ 6.3
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Foreign Currency Contract, Euro [Member]
Derivatives, Fair Value [Line Items]
Derivative, notional amount					18.9
Cash Flow Hedging [Member] \| Designated as Hedging Instrument [Member] \| Foreign Currency Contract, Pound [Member]
Derivatives, Fair Value [Line Items]
Derivative, notional amount					£ 9.2