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Derivatives And Risk Management Derivatives and Risk Management (Foreign Currency Exchange Contracts) (Details) CAD in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Caontracts	Dec. 31, 2017 CAD Caontracts	Dec. 31, 2016 USD ($) Caontracts	Dec. 31, 2016 CAD Caontracts
Schedule of Foreign Currency Derivative Contracts Outstanding [Line Items]
Number Of Days Canadian Currency Prices Are Settled With U.S. Dollars	60 days
Number of Foreign Currency Derivatives Held | Caontracts	18	18	21	21
Foreign Currency Exchange Contracts [Member] | United States of America, Dollars
Schedule of Foreign Currency Derivative Contracts Outstanding [Line Items]
Derivative, Notional Amount | $	$ 2,552		$ 2,819
Foreign Currency Exchange Contracts [Member] | Canada, Dollars
Schedule of Foreign Currency Derivative Contracts Outstanding [Line Items]
Derivative, Notional Amount | CAD		CAD 3,241		CAD 3,754

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- Definition

Number Of Days Canadian Currency Prices Are Settled With U.S. Dollars

+ References

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[Line Items] for Schedule of Foreign Currency Derivative Contracts Outstanding [Table]

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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

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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

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