Derivatives (Currency Contracts) (Details) $ in Thousands, CAD in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD
Derivative [Line Items]
Gain (loss) on derivatives not designated as hedging instruments	$ (245)	$ (158)	$ 403
Other Income (Expense) | Currency Contracts
Derivative [Line Items]
Gain (loss) on derivatives not designated as hedging instruments	$ (245)	$ (158)	$ 403
Not Designated as Hedging Instrument | Currency Contracts
Derivative [Line Items]
Derivative, notional amount | CAD				CAD 0.0	CAD 6.2