Goodwill and Other Intangible Assets (Changes in goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill at beginning of period		$ 63,934	$ 63,934	$ 72,365
Acquisitions		1,171	0	47,735
Goodwill impairment		(59,081)	0	(56,166)
Goodwill at end of period		6,024	63,934	63,934
Grain
Goodwill [Roll Forward]
Goodwill at beginning of period		0	0	46,422
Acquisitions		1,171	0	0
Goodwill impairment		0		(46,422)
Goodwill at end of period		1,171	0	0
Plant Nutrient
Goodwill [Roll Forward]
Goodwill at beginning of period		59,767	59,767	21,776
Acquisitions		0	0	47,735
Goodwill impairment	$ (2,000)	(59,081)		(9,744)
Goodwill at end of period		686	59,767	59,767
Rail
Goodwill [Roll Forward]
Goodwill at beginning of period		4,167	4,167	4,167
Acquisitions		0	0	0
Goodwill impairment		0		0
Goodwill at end of period		$ 4,167	$ 4,167	$ 4,167