Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Segment information
Consolidated revenue	$ 338,052	$ 372,903
Adjusted EBITDA	48,251	75,742
Interest expense, net	(10,358)	(5,404)
Depreciation, depletion and accretion	(27,339)	(26,040)
Income tax expense	(8,836)	(15,101)
Derivative financial instruments
Exclusion of fair value mark-to-market gains (losses)	13,652	(2,056)
Inclusion of cash amounts (received) paid	24	(524)
Total derivative financial instruments	13,676	(2,580)
Net income	15,395	26,618
Total Assets	2,404,555		2,351,323
Capital Expenditures	15,460	14,338
Total revenue from external customers by geographic location
United States	280,481	304,029
Asia	57,571	68,662
Other		212
Total revenue from external customers	338,052	372,903
Owned and Operated Mines
Segment information
Consolidated revenue	278,774	302,572
Adjusted EBITDA	45,662	67,240
Derivative financial instruments
Total Assets	1,784,968		1,826,165
Capital Expenditures	14,196	12,222
Logistics and Related Activities
Segment information
Consolidated revenue	65,870	79,553
Adjusted EBITDA	1,365	10,369
Derivative financial instruments
Total Assets	64,422		46,426
Capital Expenditures	179
Corporate and Other
Segment information
Consolidated revenue	5,828	5,698
Adjusted EBITDA	1,492	(1,727)
Derivative financial instruments
Total Assets	555,077		478,536
Capital Expenditures	1,085	2,116
Eliminations of intersegment sales
Segment information
Consolidated revenue	(12,421)	(14,920)
Adjusted EBITDA	(268)	(140)
Derivative financial instruments
Total Assets	$ 88		$ 196