Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 575,688		$ 2,451,787	$ 2,324,623
Costs, expenses and other operating
Cost of sales (exclusive of items shown separately below)	470,319		1,925,202	1,839,993
Depreciation, depletion and amortization	32,604		119,563	122,464
Accretion on asset retirement obligations	7,634		27,970	30,209
Amortization of sales contracts, net	796		11,107	53,985
Change in fair value of coal derivatives and coal trading activities, net	396		9,118	7,222
Asset impairment and mine closure costs	0		0	0
Selling, general and administrative expenses	23,193		100,300	87,952
Gain on sale of Lone Mountain Processing, Inc.	0		0	(21,297)
Other operating income, net	(5,340)		(20,611)	(30,241)
Costs, expenses and other operating	529,602		2,172,649	2,090,287
Income (loss) from operations	46,086		279,138	234,336
Interest expense, net
Interest expense	(11,241)		(20,471)	(26,905)
Interest and investment income	487		6,782	2,649
Interest expense, net	(10,754)		(13,689)	(24,256)
Income (loss) before nonoperating expenses	35,332		265,449	210,080
Nonoperating income (expense)
Non-service related pension and postretirement benefit costs	32		(3,202)	(1,940)
Net loss resulting from early retirement of debt and debt restructuring	0		(485)	(2,547)
Reorganization income (loss), net	(759)		(1,661)	(2,398)
Nonoperating income (expense)	(727)		(5,348)	(6,885)
Income before income taxes	34,605		260,101	203,195
Provision for (benefit from) income taxes	1,156		(52,476)	(35,255)
Net income	$ 33,449		$ 312,577	$ 238,450
Earnings per common share
Basic earnings per common share (in dollars per share)	$ 1.34		$ 15.90	$ 10.05
Diluted earnings per common share (in dollars per share)	$ 1.31		$ 15.15	$ 9.84
Weighted average shares outstanding
Basic weighted average shares outstanding (in shares)	25,002		19,663	23,725
Diluted weighted average shares outstanding (in shares)	25,469		20,629	24,240
Predecessor
Revenues		$ 1,398,709
Costs, expenses and other operating
Cost of sales (exclusive of items shown separately below)		1,262,174
Depreciation, depletion and amortization		191,581
Accretion on asset retirement obligations		24,321
Amortization of sales contracts, net		(728)
Change in fair value of coal derivatives and coal trading activities, net		2,856
Asset impairment and mine closure costs		129,267
Selling, general and administrative expenses		59,918
Gain on sale of Lone Mountain Processing, Inc.		0
Other operating income, net		(15,257)
Costs, expenses and other operating		1,654,132
Income (loss) from operations		(255,423)
Interest expense, net
Interest expense		(135,888)
Interest and investment income		2,653
Interest expense, net		(133,235)
Income (loss) before nonoperating expenses		(388,658)
Nonoperating income (expense)
Non-service related pension and postretirement benefit costs		(1,715)
Net loss resulting from early retirement of debt and debt restructuring		(2,213)
Reorganization income (loss), net		1,630,041
Nonoperating income (expense)		1,626,113
Income before income taxes		1,237,455
Provision for (benefit from) income taxes		(4,626)
Net income		$ 1,242,081
Earnings per common share
Basic earnings per common share (in dollars per share)		$ 58.33
Diluted earnings per common share (in dollars per share)		$ 58.28
Weighted average shares outstanding
Basic weighted average shares outstanding (in shares)		21,293
Diluted weighted average shares outstanding (in shares)		21,313