Fixed Assets (Schedule Of Fixed Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Fixed assets, at cost	$ 470,638	$ 424,056	$ 350,081
Less accumulated depreciation and amortization	204,042	195,106	171,159
Fixed assets, net	$ 266,596	$ 228,950	$ 178,922