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, 2015	Dec. 31, 2014
Predecessor [Member]
Operating activties
Net income (loss)		$ 1,242,081	$ (2,913,142)	$ (558,353)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation, depletion and amortization		191,581	379,345	418,748
Accretion on asset retirement obligations		24,321	33,680	32,909
Amortization of sales contracts, net		(728)	(8,811)	(13,187)
Prepaid royalties expensed		4,791	8,109	9,698
Deferred income taxes		(419)	(367,210)	25,152
Employee stock-based compensation expense		2,096	5,760	9,847
Gains on disposals and divestitures		(6,628)	(2,270)	(27,512)
Asset impairment and noncash mine closure costs		119,194	2,613,345	16,868
Losses from disposed operations resulting from Patriot Coal bankruptcy		0	116,343	0
Amortization relating to financing activities		12,800	25,241	17,363
Net loss resulting from early retirement of debt and debt restructuring		2,213	27,910	0
Non-cash bankruptcy reorganization items		(1,775,910)	0	0
Changes in:
Receivables		(42,786)	98,212	(8,991)
Inventories		34,440	(6,534)	41,548
Coal derivative assets and liabilities		5,678	973	5,449
Accounts payable, accrued expenses and other current liabilities		15,316	(15,532)	41,680
Asset retirement obligations		(12,041)	(17,040)	(14,621)
Pension, postretirement and other postemployment benefits		(15,692)	4,800	(25,347)
Other		(28,525)	(27,546)	(4,833)
Cash provided by (used in) operating activities		(228,218)	(44,367)	(33,582)
Investing activities
Capital expenditures		(82,434)	(119,024)	(147,286)
Minimum royalty payments		(305)	(5,871)	(7,317)
Proceeds from disposals and divestitures		(2,921)	2,191	62,358
Purchases of short term investments		(98,750)	(246,735)	(211,929)
Proceeds from sales of short term investments		185,859	290,205	205,611
Proceeds from sale of investments in equity investments and securities		1,147	2,259	9,464
Investments in and advances to affiliates, net		(3,441)	(11,502)	(16,657)
Withdrawals (deposits) of restricted cash		15,979	(91,864)	(5,678)
Cash provided by (used in) investing activities		15,134	(180,341)	(111,434)
Financing activities
Payments to retire debt		0	0	(300)
Payments on term loan		0	(19,500)	(19,500)
Net receipts (payments) on other debt		(11,986)	(11,332)	(5,395)
Debt financing costs		(23,011)	0	(4,519)
Dividends paid		0	0	(2,123)
Expenses related to debt restructuring		(2,213)	(27,910)	0
Other		0	0	(15)
Cash provided by (used in) financing activities		(37,210)	(58,742)	(31,852)
Increase (decrease) in cash and cash equivalents		(250,294)	(283,450)	(176,868)
Cash and cash equivalents, beginning of period	$ 200,487	450,781	734,231	911,099
Cash and cash equivalents, end of period		200,487	450,781	734,231
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid during the period for interest		79,979	283,337	361,727
Cash refunded during the period for income taxes, net		49	$ 4,138	$ 4,896
Successor [Member]
Operating activties
Net income (loss)	33,449
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation, depletion and amortization	32,604
Accretion on asset retirement obligations	7,634
Amortization of sales contracts, net	796
Prepaid royalties expensed	2,587
Deferred income taxes	3
Employee stock-based compensation expense	1,032
Gains on disposals and divestitures	(485)
Asset impairment and noncash mine closure costs	0
Losses from disposed operations resulting from Patriot Coal bankruptcy	0
Amortization relating to financing activities	467
Net loss resulting from early retirement of debt and debt restructuring	0
Non-cash bankruptcy reorganization items	0
Changes in:
Receivables	(22,196)
Inventories	24,870
Coal derivative assets and liabilities	1,662
Accounts payable, accrued expenses and other current liabilities	34,129
Asset retirement obligations	(4,535)
Pension, postretirement and other postemployment benefits	(5,625)
Other	(22,200)
Cash provided by (used in) operating activities	84,192
Investing activities
Capital expenditures	(15,214)
Minimum royalty payments	(63)
Proceeds from disposals and divestitures	572
Purchases of short term investments	0
Proceeds from sales of short term investments	23,000
Proceeds from sale of investments in equity investments and securities	0
Investments in and advances to affiliates, net	(823)
Withdrawals (deposits) of restricted cash	10,512
Cash provided by (used in) investing activities	17,984
Financing activities
Payments to retire debt	0
Payments on term loan	(816)
Net receipts (payments) on other debt	3,374
Debt financing costs	0
Dividends paid	0
Expenses related to debt restructuring	0
Other	151
Cash provided by (used in) financing activities	2,709
Increase (decrease) in cash and cash equivalents	104,885
Cash and cash equivalents, beginning of period	200,487
Cash and cash equivalents, end of period	305,372	$ 200,487
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid during the period for interest	39,620
Cash refunded during the period for income taxes, net	$ 287