Property, Plant And Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Cost	$ 799,970	$ 792,360
Accumulated depreciation	(284,951)	(277,330)
Net book value	515,019	515,030
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	366,236	362,283
Accumulated depreciation	(62,549)	(60,576)
Net book value	303,687	301,707
Buildings [Member]
Property, Plant and Equipment [Line Items]
Cost	258,414	256,168
Accumulated depreciation	(94,256)	(91,323)
Net book value	164,158	164,845
Yard and Automotive Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	55,038	55,352
Accumulated depreciation	(38,974)	(38,560)
Net book value	16,064	16,792
Computer Software and Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	67,311	66,265
Accumulated depreciation	(58,966)	(57,624)
Net book value	8,345	8,641
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	23,247	22,963
Accumulated depreciation	(17,149)	(16,706)
Net book value	6,098	6,257
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	20,427	20,199
Accumulated depreciation	(13,057)	(12,541)
Net book value	7,370	7,658
Assets under Development [Member]
Property, Plant and Equipment [Line Items]
Cost	9,297	9,130
Net book value	$ 9,297	$ 9,130