Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details)

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Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - Recurring Basis - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Assets    
Derivative financial instruments $ 4,454 $ 103
Liabilities    
Derivative financial instruments (7,039) (18,296)
Net Derivative Fair Value (2,585) (18,193)
Level 1    
Assets    
Derivative financial instruments 0 0
Liabilities    
Derivative financial instruments 0 0
Net Derivative Fair Value 0 0
Level 2    
Assets    
Derivative financial instruments 4,454 103
Liabilities    
Derivative financial instruments (7,039) (18,296)
Net Derivative Fair Value (2,585) (18,193)
Level 3    
Assets    
Derivative financial instruments 0 0
Liabilities    
Derivative financial instruments 0 0
Net Derivative Fair Value $ 0 $ 0