Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Supplemental Cash Flow Information [Abstract]
Interest paid	$ 9,854	$ 8,670
Noncash investing and financing activity
Capital projects incurred but not yet paid	7,115	2,216
Investment merger (decreasing equity method investments and non-controlling interest)	0	8,360
Outstanding receivable for sale of assets	0	3,597
Dividends declared not yet paid	4,663	4,501
Debt as a result of accounting standard adoption	36,953	0
Railcar assets as a result of accounting standard adoption	$ 25,643	$ 0