Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Noncash investing and financing activity
Capital projects incurred but not yet paid	$ 5,709	$ 4,930
Purchase of a productive asset through seller-financing	1,010	1,944
Purchase of Rail Group assets not yet paid	2,209	0
Shares issued for acquisition of business	4,303	0
Dividends declared not yet paid	$ 3,967	$ 3,126