Derivatives (Fair Value of Derivative Instruments and Locations in Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Current derivative asset	$ 1,064	$ 0
Non-current derivative asset	0	377
Total derivatives assets	1,064	377
Current derivative liability	(636)	(21,564)
Non-current derivative liability	(282)	(415)
Total derivative liabilities	$ 918	$ 21,979