Derivatives (Forward Contracts) (Details) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($)
Derivative [Line Items]
Notional amount	$ 184.6
Forward Contracts [Member]
Derivative [Line Items]
Realized and unrealized gains (losses)	1.2
Other Investments [Member]
Derivative [Line Items]
Derivative Liability	(1.2)
GBP
Derivative [Line Items]
Notional amount	150.0
Barclays [Member] \| Standard & Poor's, A- Rating [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	(1.2)
Notional amount	$ 184.6

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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Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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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. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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