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Derivative Financial Instruments (Textuals) (Details) € in Millions, ¥ in Millions, $ in Millions, $ in Millions | 3 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2018 USD ($) | Jun. 30, 2018 EUR (€) MBbls $ / bbl | Jun. 30, 2018 JPY (¥) | Jun. 30, 2018 USD ($) | Jun. 30, 2018 SGD ($) MBbls $ / bbl | Jun. 30, 2018 JPY (¥) MBbls $ / bbl | Jun. 30, 2018 USD ($) MBbls $ / bbl | Apr. 24, 2018 MBbls | Dec. 31, 2017 EUR (€) MBbls | Dec. 31, 2017 SGD ($) MBbls | Dec. 31, 2017 USD ($) MBbls
Debt EUR Denominated [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount, nonderivative instruments |  | € 21.0 |  | $ 24.4 |  |  |  |  |  |  |
Cumulative foreign currency translation loss |  |  |  |  |  |  | $ 0.6 |  |  |  |
Cumulative foreign currency translation loss, net of tax |  |  |  |  |  |  | 0.5 |  |  |  |
Debt Yen Denominated [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount, nonderivative instruments |  |  | ¥ 500.0 | 4.5 |  |  |  |  |  |  |
Cumulative foreign currency translation loss |  |  |  |  |  |  | 0.4 |  |  |  |
Cumulative foreign currency translation loss, net of tax |  |  |  |  |  |  | $ 0.3 |  |  |  |
Options Held [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, nonmonetary notional amount | MBbls |  | 98,658 |  |  | 98,658 | 98,658 | 98,658 | 30,612 | 125,166 | 125,166 | 125,166
Gain (Loss) related to call options | $ 0.5 |  |  | $ 0.5 |  |  |  |  |  |  |
Derivative, Average Price Risk Option Strike Price | $ / bbl |  | 73.10 |  |  | 73.10 | 73.10 | 73.10 |  |  |  |
Euro Member Countries, Euro | Forward Contracts [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount | € |  | € 10.0 |  |  |  |  |  |  | € 12.0 |  |
Singapore, Dollars | Forward Contracts [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  | $ 601.5 |  |  |  |  | $ 171.0 |
United States of America, Dollars | Forward Contracts [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  | $ 13.4 |  |  |  | $ 13.4
Long [Member] | Designated as Hedging Instrument [Member] | Singapore, Dollars | Foreign Exchange Forward [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  | $ 33.5 |  |  |  |  |  |
Long [Member] | Designated as Hedging Instrument [Member] | United States of America, Dollars | Foreign Exchange Forward [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  | 29.6 |  |  |  |
Long [Member] | Designated as Hedging Instrument [Member] | Japan, Yen | Foreign Exchange Forward [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount | ¥ |  |  |  |  |  | ¥ 5,375.7 |  |  |  |  |
Short [Member] | Designated as Hedging Instrument [Member] | Singapore, Dollars | Foreign Exchange Forward [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  | 7.3 |  |  |  |  | 16.3 |  |  |  |
Short [Member] | Designated as Hedging Instrument [Member] | United States of America, Dollars | Foreign Exchange Forward [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  | 24.4 |  |  |  |  | 0.0 |  |  |  |
Short [Member] | Designated as Hedging Instrument [Member] | Japan, Yen | Foreign Exchange Forward [Member] |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  | € 17.9 |  |  |  |  | $ 28.2 |  |  |  |

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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + 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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