Commitments (Schedule of Capital Leased Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Capital Leased Assets [Line Items]
Cost	$ 9,100	$ 6,395
Accumulated depreciation	(5,132)	(4,203)
Net book value	3,968	2,192
Computer Software and Equipment [Member]
Capital Leased Assets [Line Items]
Cost	8,511	6,080
Accumulated depreciation	(4,990)	(4,132)
Net book value	3,521	1,948
Yard and Auto Equipment [Member]
Capital Leased Assets [Line Items]
Cost	589	315
Accumulated depreciation	(142)	(71)
Net book value	$ 447	$ 244