Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Item	Jun. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Reported segment | Item			2
Revenues Abstract
Consolidated revenue	$ 229,201	$ 174,188	$ 424,930	$ 355,437
Capital Expenditures
Capital Expenditures			11,372	15,342
Net income (loss)	(6,948)	35,289	(27,056)	(1,086)
Interest Income	(118)	(33)	(157)	(70)
Interest expense, net	9,866	11,286	22,778	22,338
Other, Net	138	206	448	595
Income tax benefit (expense)	(149)	(1,158)	151	(2,580)
(Income) loss from unconsolidated affiliates, net of tax	(305)	330	(632)	1,078
Consolidated operating income (loss)	2,484	45,920	(4,468)	20,275
Depreciation and depletion	19,249	(19,510)	37,894	(408)
Accretion	1,846	1,994	3,667	4,576
Impairments	0	34	0	4,187
Derivative financial instruments
Exclusion of fair value mark-to-market gains (losses)	(1,595)	8,286	(3,939)	6,325
Inclusion of cash amounts (received) paid			1,147	2,640
Debt restructuring costs	0	0	0	0
Other	(138)	(206)	(448)	(595)
Operating Income (Loss)	2,484	45,920	(4,468)	20,275
Intersegment Elimination
Revenues Abstract
Consolidated revenue	(16,561)	(801)	(23,983)	(4,667)
Capital Expenditures
Consolidated operating income (loss)	460	(55)	18	(113)
Derivative financial instruments
Adjusted EBITDA	460	(55)	18	(113)
Operating Income (Loss)	460	(55)	18	(113)
Owned and Operated Mines
Revenues Abstract
Consolidated revenue	178,644	152,105	352,254	319,269
Capital Expenditures
Capital Expenditures			10,536	13,978
Other, Net	138	207	448	595
Consolidated operating income (loss)	15,319	49,154	27,237	43,719
Depreciation and depletion	19,061	(19,854)	37,513	(1,071)
Accretion	1,695	1,891	3,365	4,318
Impairments		(32)		2,200
Derivative financial instruments
Exclusion of fair value mark-to-market gains (losses)	1,595	(8,276)	3,939	(6,275)
Inclusion of cash amounts (received) paid	(811)	(2,112)	(1,147)	(6,202)
Total derivative financial instruments	784	(10,388)	2,792	(12,477)
Other	(138)	(207)	(448)	(595)
Adjusted EBITDA	36,721	20,564	70,459	36,033
Operating Income (Loss)	15,319	49,154	27,237	43,719
Logistics and Related Activities
Revenues Abstract
Consolidated revenue	65,977	3,200	94,225	17,218
Capital Expenditures
Other, Net	0	894	0	1,753
Consolidated operating income (loss)	(3,440)	(8,240)	(10,855)	(16,061)
Derivative financial instruments
Exclusion of fair value mark-to-market gains (losses)	0	(10)	0	(50)
Inclusion of cash amounts (received) paid	0	1,781	0	3,563
Total derivative financial instruments	0	1,771	0	3,513
Non-cash throughput amortization expense and contract termination payments	5,069	0	9,920	0
Other	0	(894)	0	(1,753)
Adjusted EBITDA	1,629	(7,363)	(935)	(14,301)
Operating Income (Loss)	(3,440)	(8,240)	(10,855)	(16,061)
Corporate and Other
Revenues Abstract
Consolidated revenue	1,141	19,684	2,434	23,617
Capital Expenditures
Capital Expenditures			836	1,364
Other, Net	(305)	(565)	(632)	(676)
Consolidated operating income (loss)	(9,855)	5,062	(20,868)	(7,270)
Depreciation and depletion	188	343	380	663
Accretion	151	103	302	258
Impairments	0	66	0	2,048
Derivative financial instruments
Debt restructuring costs	(17)	0	23	0
Non-cash throughput amortization expense and contract termination payments	0	0	0	0
Other	305	565	632	676
Adjusted EBITDA	(9,228)	6,139	(19,531)	(3,625)
Operating Income (Loss)	(9,855)	5,062	(20,868)	(7,270)
Contract Buyout Proceeds	$ 48	$ 18,823	$ 96	$ 22,754