Income Taxes (Expected Income Tax) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Expected amount	$ 4,868	$ 2,966	$ 9,653
Adjustment to deferred taxes from the Tax Act rate reduction	(17,974)
Change in Indiana rate			(85)
State income taxes, net of federal benefit	115	(387)	612
Percentage depletion	(4,128)	(6,021)	(2,606)
Stock-based compensation	(204)	(238)
Captive insurance	(379)	(418)	(419)
Adjustments to NOL carryforwards	(1,038)
Return to provision adjustment	(205)
Other	(249)	72	283
Total tax expected	$ (19,194)	$ (4,026)	$ 7,438