Fixed Assets (Schedule Of Fixed Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Property, Plant and Equipment [Abstract]
Fixed assets, at cost	$ 496,701	$ 424,056	$ 381,650
Less accumulated depreciation and amortization	214,559	195,106	178,446
Fixed assets, net	$ 282,142	$ 228,950	$ 203,204