Consolidated Condensed Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues	$ 570,289	$ 525,134	$ 497,421
Costs and expenses:
Cost of goods sold	408,772	390,666	382,252
Selling, general and administrative expenses	50,397	49,419	40,549
Environmental remediation charge	3,522	0	1,200
Asset impairment charge	0	107	1,180
Total costs and expenses	462,691	440,192	425,181
Operating income	107,598	84,942	72,240
Interest expense, net	(23,132)	(25,539)	(27,829)
Income before income taxes	84,466	59,403	44,411
Income tax provision	(13,885)	(16,809)	(4,145)
Net income	$ 70,581	$ 42,594	$ 40,266
Net income per common share:
Basic (in dollars per share)	$ 1.74	$ 1.06	$ 1.00
Diluted (in dollars per share)	$ 1.73	$ 1.05	$ 1.00
Distributions per share (in dollars per share)	$ 1.28	$ 1.24	$ 1.84