Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Offsetting Assets and Liabilities [Line Items]
Derivative Assets	$ 65,114	$ 406
Derivative Liabilities	(17,920)	(29,028)
Not Designated as Hedging Instrument
Offsetting Assets and Liabilities [Line Items]
Derivative Assets	65,114	406
Derivative Liabilities	(17,920)	(29,028)
Not Designated as Hedging Instrument | Current Assets
Offsetting Assets and Liabilities [Line Items]
Derivative asset, fair value, gross asset	78,091	406
Derivative asset, fair value, gross liability	(12,977)	0
Derivative Assets	65,114	406
Not Designated as Hedging Instrument | Current Liabilities
Offsetting Assets and Liabilities [Line Items]
Derivative liability, fair value, gross liability	(23,457)	(27,744)
Derivative liability, fair value, gross asset	12,977	0
Derivative Liabilities	(10,480)	(27,744)
Not Designated as Hedging Instrument | Non-current Liabilities
Offsetting Assets and Liabilities [Line Items]
Derivative liability, fair value, gross liability	(7,440)	(1,284)
Derivative liability, fair value, gross asset	0	0
Derivative Liabilities	$ (7,440)	$ (1,284)