Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing activities
Debt financing costs	$ (2,000)	$ (2,200)
Cash and cash equivalents, beginning of period	305,372
Cash and cash equivalents, end of period	347,580
Successor [Member]
Operating activities
Net income (loss)	51,668
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation, depletion and amortization	31,921
Accretion on asset retirement obligations	7,623
Amortization of sales contracts, net	14,690
Prepaid royalties expensed	2,281
Deferred income taxes	5,830
Employee stock-based compensation expense	2,426
Gains on disposals and divestitures, net	(347)
Asset impairment and non-cash mine closure costs	0
Net loss resulting from early retirement of debt and debt restructuring	2,030
Non-cash bankruptcy reorganization items	0
Amortization relating to financing activities	535
Changes in:
Receivables	37,134
Inventories	(11,732)
Accounts payable, accrued expenses and other current liabilities	(20,529)
Income taxes, net	(4,965)
Other	6,964
Cash provided by (used in) operating activities	125,529
Investing activities
Capital expenditures	(5,950)
Minimum royalty payments	(63)
Proceeds from disposals and divestitures	420
Purchases of short term investments	(78,523)
Proceeds from sales of short term investments	45,886
Investments in and advances to affiliates, net	(7,905)
Withdrawals (deposits) of restricted cash	2,066
Cash used in investing activities	(44,069)
Financing activities
Proceeds from issuance of term loan due 2024	298,500
Payments to extinguish term loan due 2021	(325,684)
Net payments on other debt	(2,810)
Debt financing costs	(7,228)
Net loss resulting from early retirement of debt and debt restructuring	(2,030)
Cash used in financing activities	(39,252)
Increase (decrease) in cash and cash equivalents	42,208
Cash and cash equivalents, beginning of period	305,372
Cash and cash equivalents, end of period	$ 347,580
Predecessor [Member]
Operating activities
Net income (loss)		(206,702)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation, depletion and amortization		63,699
Accretion on asset retirement obligations		8,306
Amortization of sales contracts, net		(833)
Prepaid royalties expensed		1,286
Deferred income taxes		(429)
Employee stock-based compensation expense		1,003
Gains on disposals and divestitures, net		1
Asset impairment and non-cash mine closure costs		77,550
Net loss resulting from early retirement of debt and debt restructuring		2,213
Non-cash bankruptcy reorganization items		(13,892)
Amortization relating to financing activities		3,150
Changes in:
Receivables		7,815
Inventories		734
Accounts payable, accrued expenses and other current liabilities		39,441
Income taxes, net		(642)
Other		7,202
Cash provided by (used in) operating activities		(10,098)
Investing activities
Capital expenditures		(5,926)
Minimum royalty payments		(71)
Proceeds from disposals and divestitures		0
Purchases of short term investments		(55,132)
Proceeds from sales of short term investments		56,134
Investments in and advances to affiliates, net		(2,156)
Withdrawals (deposits) of restricted cash		(12,108)
Cash used in investing activities		(19,259)
Financing activities
Net payments on other debt		(5,410)
Debt financing costs		(18,403)
Net loss resulting from early retirement of debt and debt restructuring		(2,213)
Cash used in financing activities		(26,026)
Increase (decrease) in cash and cash equivalents		(55,383)
Cash and cash equivalents, beginning of period		450,781
Cash and cash equivalents, end of period		$ 395,398