Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments - Gain (Loss) on Derivatives (Details)

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Derivative Financial Instruments - Gain (Loss) on Derivatives (Details) - Swap agreements as of December 31, 2017 - Cash Flow Hedging - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Derivative [Line Items]    
Gain (Loss) Recognized in OCI $ 318 $ 400
Interest expense and other    
Derivative [Line Items]    
Gain (Loss) Recognized in Income (77) 136
Gain (Loss) Recognized in Income $ (54) $ 152