Derivative Instruments (Fair Value of Cash Flow and Fair Value Derivative Instruments) (Details) - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 13	$ 247
Liability Derivatives, Fair Value		91
Fair Value Hedging [Member] | Interest rate contracts [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	13	32
Fair Value Hedging [Member] | Interest rate contracts [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value		215
Liability Derivatives, Fair Value		91
Cash Flow Hedging [Member] | Interest rate contracts [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 1,156	$ 1,148