Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Noncash investing and financing activity
Capital projects incurred but not yet paid	$ 9,653	$ 5,709
Purchase of a productive asset through seller-financing	0	1,010
Purchase of Rail Group assets not yet paid	0	2,209
Shares issued for acquisition of business	0	4,303
Dividends declared not yet paid	$ 4,341	$ 3,967