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