Commitments (Schedule of Capital Leased Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Capital Leased Assets [Line Items]
Cost	$ 21,553	$ 15,192
Accumulated depreciation	(6,577)	(4,500)
Net book value	14,976	10,692
Computer Software and Equipment [Member]
Capital Leased Assets [Line Items]
Cost	9,428	8,699
Accumulated depreciation	(3,992)	(3,604)
Net book value	5,436	5,095
Yard and Auto Equipment [Member]
Capital Leased Assets [Line Items]
Cost	12,125	6,493
Accumulated depreciation	(2,585)	(896)
Net book value	$ 9,540	$ 5,597