Derivatives And Risk Management Derivatives and Risk Management (Foreign Currency Exchange Contracts) (Details) CAD in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2017 CAD derivative_contracts	Sep. 30, 2017 USD ($) derivative_contracts	Dec. 31, 2016 CAD derivative_contracts	Dec. 31, 2016 USD ($) 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	19	19	21	21
United States of America, Dollars | Foreign Exchange Contract [Member]
Foreign Currency Fair Value Hedge Derivative [Line Items]
Derivative, Notional Amount | $		$ 3,198		$ 2,819
Canada, Dollars | Foreign Exchange Contract [Member]
Foreign Currency Fair Value Hedge Derivative [Line Items]
Derivative, Notional Amount | CAD	CAD 3,925		CAD 3,754