Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues	$ 174,475	$ 177,215	$ 437,347	$ 460,713
Costs and expenses:
Cost of goods sold	136,072	121,574	353,285	322,016
Selling, general and administrative expenses	10,689	10,772	35,010	32,794
Total costs and expenses	146,761	132,346	388,295	354,810
Operating income	27,714	44,869	49,052	105,903
Interest expense, net	(8,335)	(5,506)	(24,420)	(16,475)
Income tax benefit (provision)	19,379	39,363	24,632	89,428
Income taxes	2,419	(6,209)	3,533	(19,654)
Net income	$ 21,798	$ 33,154	$ 28,165	$ 69,774
Net income per share:
Basic (in dollars per share)	$ 0.53	$ 0.81	$ 0.69	$ 1.71
Diluted (in dollars per share)	0.53	0.81	0.69	1.71
Distributions per share (in dollars per share)	$ 0.375	$ 0.35	$ 1.125	$ 1.05
Weighted-average shares outstanding (in thousands):
Basic (in shares)	40,846,315	40,744,667	40,831,296	40,732,704
Diluted (in shares)	40,985,088	40,889,280	40,966,869	40,860,978