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Derivatives And Risk Management Derivatives and Risk Management (Foreign Currency Exchange Contracts) (Details) $ in Thousands, $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2018 CAD ($) derivative_contracts | Mar. 31, 2018 USD ($) derivative_contracts | Dec. 31, 2017 CAD ($) derivative_contracts | Dec. 31, 2017 USD ($) derivative_contracts
Foreign Currency Fair Value Hedge Derivative [Line Items] |  |  |  |
Number Of Days Canadian Currency Prices Are Settled With U.S. Dollars | 60 days |  |  |
Number of Foreign Currency Derivatives Held | derivative_contracts | 23 | 23 | 18 | 18
United States of America, Dollars | Foreign Exchange Contract [Member] |  |  |  |
Foreign Currency Fair Value Hedge Derivative [Line Items] |  |  |  |
Derivative, Notional Amount |  | $ 5,312 |  | $ 2,552
Canada, Dollars | Foreign Exchange Contract [Member] |  |  |  |
Foreign Currency Fair Value Hedge Derivative [Line Items] |  |  |  |
Derivative, Notional Amount | $ 6,866 |  | $ 3,241 |

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + 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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- Definition Number of foreign currency exchange rate derivatives held by the entity at the reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959 + Details
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