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) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Assets    
Derivative financial instruments $ 2,299 $ 0
Recurring Basis    
Assets    
Derivative financial instruments 13,868 406
Liabilities    
Derivative financial instruments (47,084) (29,028)
Net Derivative Fair Value (33,216) (28,622)
Recurring Basis | Level 1    
Assets    
Derivative financial instruments 0 0
Liabilities    
Derivative financial instruments 0 0
Net Derivative Fair Value 0 0
Recurring Basis | Level 2    
Assets    
Derivative financial instruments 13,868 406
Liabilities    
Derivative financial instruments (47,084) (29,028)
Net Derivative Fair Value (33,216) (28,622)
Recurring Basis | Level 3    
Assets    
Derivative financial instruments 0 0
Liabilities    
Derivative financial instruments 0 0
Net Derivative Fair Value $ 0 $ 0