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Share Capital Narrative (Details) - USD ($)			6 Months Ended
	Jun. 30, 2018	Oct. 03, 2016	Jun. 30, 2018
Equity, Class of Treasury Stock [Line Items]
Ordinary shares repurchased	3,482,469		464,055
Ordinary shares repurchased, value	$ 297,300,000		$ 54,200,000
Buyback Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount		$ 400,000,000
Buyback Program | Maximum
Equity, Class of Treasury Stock [Line Items]
Share repurchase program, authorized percentage		10.00%

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Amount of stock repurchase plan authorized.

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Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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