Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Consolidated revenue	$ 301,673	$ 342,337	$ 863,374	$ 982,253
Adjusted EBITDA	39,257	46,023	90,435	131,799
Interest expense, net	(10,947)	(12,664)	(36,137)	(64,286)
Depreciation and depletion	(7,896)	(25,815)	(51,742)	(81,944)
Amortization of port access contract rights	(928)	0	(2,783)	0
Accretion	(3,070)	(3,848)	(9,960)	(12,066)
Income tax benefit (expense)	2,205	(40,688)	12,350	(30,709)
Tax agreement benefit	0	58,595	0	58,595
Derivative financial instruments
Exclusion of fair value mark-to-market gains (losses)	(10,235)	515	(17,781)	16,052
Inclusion of cash amounts (received) paid	724	(5,007)	1,618	(16,905)
Total derivative financial instruments	(9,511)	(4,492)	(16,164)	(852)
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	0	0	(33,355)	0
Gain on sale of Decker Mine interest	0	74,262	0	74,262
Net income (loss)	8,873	91,069	(48,704)	73,295
Total Assets
Total Assets	1,998,684		1,998,684		$ 2,151,153
Capital Expenditures
Capital Expenditures			35,838	58,326
Intersegment Elimination
Segment Reporting Information [Line Items]
Consolidated revenue	(10,931)	(17,075)	(41,789)	(44,692)
Adjusted EBITDA	(237)	(304)	(1,349)	(1,503)
Total Assets
Total Assets	(157)		(157)		(307)
Capital Expenditures
Capital Expenditures			0	0
Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	301,673	342,337	863,374	982,253
United States | Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	265,531	284,843	726,340	819,562
South Korea | Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	29,252	48,945	114,734	127,370
Other | Reportable Geographical Components [Member]
Segment Reporting Information [Line Items]
Consolidated revenue	6,890	8,549	22,300	35,321
Owned and Operated Mines
Segment Reporting Information [Line Items]
Consolidated revenue	265,657	285,983	733,735	827,680
Adjusted EBITDA	57,795	43,589	119,221	126,741
Total Assets
Total Assets	1,594,188		1,594,188		1,704,267
Capital Expenditures
Capital Expenditures			32,640	17,534
Logistics and Related Activities
Segment Reporting Information [Line Items]
Consolidated revenue	44,772	65,640	162,802	178,836
Adjusted EBITDA	(19,050)	1,394	(33,780)	4,465
Total Assets
Total Assets	86,356		86,356		92,347
Capital Expenditures
Capital Expenditures			0	37,100
Corporate and Other
Segment Reporting Information [Line Items]
Consolidated revenue	2,176	7,789	8,626	20,429
Adjusted EBITDA	512	$ 1,040	4,994	593
Total Assets
Total Assets	$ 318,297		318,297		$ 354,846
Capital Expenditures
Capital Expenditures			$ 3,198	$ 3,692