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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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- Definition 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 + Details
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