Property, Plant And Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Cost	$ 814,660	$ 792,360
Accumulated depreciation	(290,448)	(277,330)
Net book value	524,212	515,030
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	372,966	362,283
Accumulated depreciation	(64,957)	(60,576)
Net book value	308,009	301,707
Buildings [Member]
Property, Plant and Equipment [Line Items]
Cost	262,153	256,168
Accumulated depreciation	(97,815)	(91,323)
Net book value	164,338	164,845
Yard and Automotive Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	58,343	55,352
Accumulated depreciation	(39,349)	(38,560)
Net book value	18,994	16,792
Computer Software and Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	64,951	66,265
Accumulated depreciation	(56,647)	(57,624)
Net book value	8,304	8,641
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	24,427	22,963
Accumulated depreciation	(17,843)	(16,706)
Net book value	6,584	6,257
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	21,017	20,199
Accumulated depreciation	(13,837)	(12,541)
Net book value	7,180	7,658
Assets under Development [Member]
Property, Plant and Equipment [Line Items]
Cost	10,803	9,130
Net book value	$ 10,803	$ 9,130