CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income (loss)	$ (6,639)	$ 21,841	$ (204,900)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion, and amortization	72,270	27,218	69,774
Accretion	7,072	6,645	12,555
Impairments	0	4,609	91,541
Loss (income) from unconsolidated affiliates, net of tax	(713)	(657)	(1,200)
Distributions of income from unconsolidated affiliates	4,530	1,515	0
Deferred income taxes	0	(971)	79,486
Equity-based compensation expense	11,730	13,064	6,935
(Gain) loss on derivative financial instruments	2,672	(8,180)	30,635
Cash received (paid) on derivative financial instruments settlements	(1,920)	(3,305)	(585)
Premium payments on derivative financial instruments	0	0	(5,813)
Non-cash interest expense related to early retirement of debt and refinancings	702	1,254	0
Net periodic postretirement benefit costs	(5,471)	(1,841)	8,096
Addback of debt restructuring costs	23	4,665	0
Payments for logistics contracts	(22,938)	(30,500)	(37,500)
Logistics throughput contract amortization expense	35,839	32,667	0
Other	7,818	3,798	16,736
Changes in operating assets and liabilities:
Accounts receivable	(764)	(8,889)	44,012
Inventories, net	(4,359)	8,047	3,153
Income tax receivable	(29,454)	0	0
Other assets	(10,680)	16,057	(18,202)
Other liabilities	(7,682)	(38,321)	(53,134)
Net cash provided by (used in) operating activities	52,036	48,716	41,589
Investing activities
Purchases of property, plant and equipment	(13,097)	(33,639)	(37,662)
Cash paid for capitalized interest	0	(1,444)	(843)
Investment in port access rights	0	0	(2,160)
Investment in development projects	(1,750)	(1,500)	(1,526)
Investment in unconsolidated affiliate	0	0	(6,570)
Payment of restricted cash	0	(725)	(6,500)
Return of restricted cash	0	8,500	0
Insurance proceeds	0	2,826	0
Other	195	659	223
Net cash provided by (used in) investing activities	(14,652)	(25,323)	(55,038)
Financing activities
Principal payments on federal coal leases	0	0	(63,970)
Repayment of senior notes	(62,094)	0	0
Payment of debt refinancing costs	(408)	0	0
Payments of deferred financing costs	0	(3,624)	(342)
Payment amortized to deferred gain	(12,395)	0	0
Cash Paid on tender of 2019 and 2024 senior notes	0	(18,335)	0
Payment of debt restructuring costs	(23)	(4,665)	0
Proceeds from issuance of common stock	68,850	0	0
Cash paid for equity offering	(4,490)	0	0
Other	(2,584)	(2,374)	(1,671)
Net cash provided by (used in) financing activities	(13,144)	(28,998)	(65,983)
Net increase (decrease) in cash and cash equivalents	24,240	(5,605)	(79,432)
Cash and cash equivalents at beginning of period	83,708	89,313	168,745
Cash and cash equivalents at end of period	107,948	83,708	89,313
Supplemental cash flow disclosures
Interest paid	33,681	39,560	46,445
Income taxes paid (refunded)	(1,459)	(8,443)	10,049
Supplemental noncash investing and financing activities
Capital expenditures included in accounts payable	1,154	3,227	682
Assets acquired under capital leases	0	964	1,568
Debt restructuring of 2019 and 2024 senior notes (Note 11)	$ 0	(290,366)	$ 0
Debt issuance of 2021 senior notes (Note 11)		$ 290,366