Property, Plant And Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Cost	$ 859,733	$ 824,354
Accumulated depreciation	(367,606)	(339,872)
Net book value	492,127	484,482
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	370,511	361,623
Accumulated depreciation	(81,591)	(77,015)
Net book value	288,920	284,608
Buildings [Member]
Property, Plant and Equipment [Line Items]
Cost	259,928	252,774
Accumulated depreciation	(125,944)	(115,423)
Net book value	133,984	137,351
Yard and Automotive Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	74,151	66,871
Accumulated depreciation	(47,663)	(40,686)
Net book value	26,488	26,185
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	86,423	80,756
Accumulated depreciation	(72,169)	(68,431)
Net book value	14,254	12,325
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	35,587	31,760
Accumulated depreciation	(24,729)	(21,776)
Net book value	10,858	9,984
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	21,654	19,756
Accumulated depreciation	(15,510)	(16,541)
Net book value	6,144	3,215
Assets under Development [Member]
Property, Plant and Equipment [Line Items]
Cost	11,479	10,814
Net book value	$ 11,479	$ 10,814