Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Operating activties
Net income (loss)	$ 33,449		$ 238,450
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation, depletion and amortization	32,604		122,464
Accretion on asset retirement obligations	7,634		30,209
Amortization of sales contracts, net	796		53,985
Prepaid royalties expensed	2,587		2,905
Deferred income taxes	3		(21,965)
Employee stock-based compensation expense	1,032		10,437
Gains on disposals and divestitures	(485)		(24,327)
Asset impairment and noncash mine closure costs	0		0
Losses from disposed operations resulting from Patriot Coal bankruptcy	0		0
Amortization relating to financing activities	467		3,736
Net loss resulting from early retirement of debt and debt restructuring	0		2,547
Non-cash bankruptcy reorganization items	0		0
Changes in:
Receivables	(22,196)		8,370
Inventories	24,870		(19,626)
Coal derivative assets and liabilities	1,662		6,040
Accounts payable, accrued expenses and other current liabilities	34,129		17,173
Asset retirement obligations	(4,535)		(20,584)
Pension, postretirement and other postemployment benefits	(5,625)		(15,253)
Other	(22,200)		1,912
Cash provided by (used in) operating activities	84,192		396,473
Investing activities
Capital expenditures	(15,214)		(59,205)
Minimum royalty payments	(63)		(5,296)
Proceeds from disposals and divestitures	572		12,920
Purchases of short term investments	0		(258,948)
Proceeds from sales of short term investments	23,000		190,064
Proceeds from sale of investments in equity investments and securities	0		0
Investments in and advances to affiliates, net	(823)		(10,173)
Withdrawals (deposits) of restricted cash	10,512		70,836
Cash provided by (used in) investing activities	17,984		(59,802)
Financing activities
Proceeds from issuance of term loan due 2024	0		298,500
Payments to extinguish term loan due 2021	0		(325,684)
Payments on term loan	(816)		(2,250)
Net receipts (payments) on other debt	3,374		(694)
Debt financing costs	0		(10,149)
Dividends paid	0		(24,369)
Purchases of treasury stock	0		(301,512)
Expenses related to debt restructuring	0		(2,360)
Other	151		(138)
Cash provided by (used in) financing activities	2,709		(368,656)
Increase (decrease) in cash and cash equivalents	104,885		(31,985)
Cash and cash equivalents, beginning of period	200,487		305,372
Cash and cash equivalents, end of period	305,372	$ 200,487	273,387
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid during the period for interest	39,620		34,691
Cash refunded during the period for income taxes, net	287		$ 7,958
Predecessor
Operating activties
Net income (loss)		1,242,081		$ (2,913,142)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation, depletion and amortization		191,581		379,345
Accretion on asset retirement obligations		24,321		33,680
Amortization of sales contracts, net		(728)		(8,811)
Prepaid royalties expensed		4,791		8,109
Deferred income taxes		(419)		(367,210)
Employee stock-based compensation expense		2,096		5,760
Gains on disposals and divestitures		(6,628)		(2,270)
Asset impairment and noncash mine closure costs		119,194		2,613,345
Losses from disposed operations resulting from Patriot Coal bankruptcy		0		116,343
Amortization relating to financing activities		12,800		25,241
Net loss resulting from early retirement of debt and debt restructuring		2,213		27,910
Non-cash bankruptcy reorganization items		(1,775,910)		0
Changes in:
Receivables		(42,786)		98,212
Inventories		34,440		(6,534)
Coal derivative assets and liabilities		5,678		973
Accounts payable, accrued expenses and other current liabilities		15,316		(15,532)
Asset retirement obligations		(12,041)		(17,040)
Pension, postretirement and other postemployment benefits		(15,692)		4,800
Other		(28,525)		(27,546)
Cash provided by (used in) operating activities		(228,218)		(44,367)
Investing activities
Capital expenditures		(82,434)		(119,024)
Minimum royalty payments		(305)		(5,871)
Proceeds from disposals and divestitures		(2,921)		2,191
Purchases of short term investments		(98,750)		(246,735)
Proceeds from sales of short term investments		185,859		290,205
Proceeds from sale of investments in equity investments and securities		1,147		2,259
Investments in and advances to affiliates, net		(3,441)		(11,502)
Withdrawals (deposits) of restricted cash		15,979		(91,864)
Cash provided by (used in) investing activities		15,134		(180,341)
Financing activities
Proceeds from issuance of term loan due 2024		0		0
Payments to extinguish term loan due 2021		0		0
Payments on term loan		0		(19,500)
Net receipts (payments) on other debt		(11,986)		(11,332)
Debt financing costs		(23,011)		0
Dividends paid		0		0
Purchases of treasury stock		0		0
Expenses related to debt restructuring		(2,213)		(27,910)
Other		0		0
Cash provided by (used in) financing activities		(37,210)		(58,742)
Increase (decrease) in cash and cash equivalents		(250,294)		(283,450)
Cash and cash equivalents, beginning of period	$ 200,487	450,781		734,231
Cash and cash equivalents, end of period		200,487		450,781
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid during the period for interest		79,979		283,337
Cash refunded during the period for income taxes, net		$ 49		$ 4,138