Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Consolidated revenue	$ 244,148		$ 320,850	$ 561,701	$ 639,916
Adjusted EBITDA	11,100		46,075	51,177	85,774
Interest expense, net	(12,571)		(13,752)	(25,190)	(51,622)
Depreciation and depletion	(19,310)		(29,200)	(43,846)	(56,128)
Amortization of port access contract rights	(928)		0	(1,855)	0
Accretion	(3,348)		(4,088)	(6,890)	(8,217)
Income tax benefit (expense)	9,866		3,489	10,146	9,979
Tax agreement benefit (expense)	0		0
Derivative financial instruments
Exclusion of fair value mark-to-market gains (losses)	(2,761)		2,803	(7,546)	15,537
Inclusion of cash amounts (received) paid	(1,135)		(6,628)	894	(11,898)
Total derivative financial instruments	(3,896)		(3,825)	(6,652)	3,640
FN 4-Excludes premiums paid in prior periods for contracts settled	5,813		0	5,813	0
FN 5-Excludes premiums paid at contract inception	992		0	2,976	0
Goodwill impairment	(33,355)		0	(33,355)	0
Gain on sale of Decker Mine interest	0	$ 74,300	0
Net income (loss)	(52,897)		(2,148)	(57,577)	(17,774)
Total Assets
Total Assets	1,993,523			1,993,523		$ 2,159,918
Capital Expenditures
Capital Expenditures				24,512	10,770
Intersegment Elimination
Segment Reporting Information [Line Items]
Consolidated revenue	(11,941)		(14,198)	(30,858)	(27,617)
Adjusted EBITDA	(456)		(848)	(1,112)	(1,199)
Total Assets
Total Assets	(47)			(47)		(307)
Capital Expenditures
Capital Expenditures				0	0
Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	244,148		320,850	561,701	639,916
United States | Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	202,675		267,489	460,809	534,718
South Korea | Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	35,470		27,482	85,481	78,425
Other | Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	6,003		25,879	15,411	26,773
Owned and Operated Mines
Segment Reporting Information [Line Items]
Consolidated revenue	206,279		272,099	468,078	541,698
Adjusted EBITDA	17,130		41,956	61,426	83,152
Total Assets
Total Assets	1,631,506			1,631,506		1,704,267
Capital Expenditures
Capital Expenditures				22,327	8,930
Logistics and Related Activities
Segment Reporting Information [Line Items]
Consolidated revenue	48,591		54,683	118,031	113,196
Adjusted EBITDA	(6,392)		2,699	(14,730)	3,070
Total Assets
Total Assets	87,627			87,627		92,347
Capital Expenditures
Capital Expenditures				0	0
Corporate and Other
Segment Reporting Information [Line Items]
Consolidated revenue	1,219		8,267	6,450	12,639
Adjusted EBITDA	362		$ 1,420	4,481	(448)
Total Assets
Total Assets	$ 274,437			274,437		$ 363,611
Capital Expenditures
Capital Expenditures				$ 2,185	$ 1,840