Property And Equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Depreciation expense	$ 25,561	$ 24,331	$ 20,979
Impairment of assets	2,427	8,618	544,611
Property, Plant and Equipment [Member]
Impairment of assets	$ 636	$ 7,408	$ 614