Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues	$ 128,747	$ 143,919	$ 262,872	$ 283,498
Costs and expenses:
Cost of goods sold	109,441	101,849	217,213	200,442
Selling, general and administrative expenses	11,995	12,345	24,321	22,022
Total costs and expenses	121,436	114,194	241,534	222,464
Operating income	7,311	29,725	21,338	61,034
Interest expense, net	(8,016)	(5,509)	(16,085)	(10,969)
Income (loss) before income taxes	(705)	24,216	5,253	50,065
Income taxes	1,416	(7,946)	1,114	(13,445)
Net income	$ 711	$ 16,270	$ 6,367	$ 36,620
Net income per share:
Basic (in dollars per share)	$ 0.02	$ 0.40	$ 0.16	$ 0.90
Diluted (in dollars per share)	0.02	0.40	0.16	0.90
Distributions per share (in dollars per share)	$ 0.375	$ 0.35	$ 0.75	$ 0.70
Weighted-average shares outstanding (in thousands):
Basic (in shares)	40,842,672	40,740,979	40,822,326	40,726,397
Diluted (in shares)	40,963,488	40,850,253	40,932,852	40,833,041