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Risk Management and Derivatives (Narrative) (Details) - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Derivative [Line Items]      
Notional amount $ 751,700,000    
Minimum maturity 1 month    
Maximum maturity 13 months    
Foreign currency cash flow hedges reclassified $ 2,000,000 $ 800,000  
Interest Rate Swap [Member]      
Derivative [Line Items]      
Notional amount 131,300,000    
Derivative gain(loss) 22,700 349,400  
Fair Value, Inputs, Level 2 [Member]      
Derivative [Line Items]      
Foreign currency contract liabilities (7,293,000)   $ (6,818,000)
Foreign currency contract assets   5,801,000  
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]      
Derivative [Line Items]      
Fair value of interest rate derivatives $ 2,103,000 $ 162,000 $ 1,088,000