Quarterly Selected Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended											6 Months Ended	9 Months Ended	12 Months Ended
	Oct. 01, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2015	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Class of Stock [Line Items]
Revenues						$ 575,688									$ 2,324,623
Asset impairment and mine closure costs						0				$ 500,000	$ 2,100,000	$ 19,100	$ 2,600,000		0
Income (loss) from operations						46,118									232,396
Net income (loss)						$ 33,449									$ 238,450
Diluted earnings (loss) per common share (in dollars per share)						$ 1.31									$ 9.84
Predecessor
Class of Stock [Line Items]
Revenues			$ 613,538	$ 549,866	$ 600,975		$ 550,305	$ 420,298	$ 428,106					$ 1,398,709		$ 2,573,260
Gross profit			65,100	62,577	85,747		31,042	(56,469)	(53,325)
Asset impairment and mine closure costs							46	43,701	85,520					129,267		2,628,303
Income (loss) from operations			72,489	42,692	66,264		11,795	(110,521)	(158,412)					(257,138)		(2,865,063)
Reorganization items, net	$ 1,676,091		(43)	(21)	(2,828)	$ (759)	(20,904)	(21,271)	(3,875)					1,630,041		0
Net income (loss)	$ 1,676,091		$ 68,351	$ 37,160	$ 51,668		$ (51,421)	$ (175,887)	$ (206,702)					$ 1,242,081		$ (2,913,142)
Diluted earnings (loss) per common share (in dollars per share)	$ 78.66		$ 2.83	$ 1.48	$ 2.03		$ (2.41)	$ (8.26)	$ (9.71)					$ 58.28		$ (136.86)
Successor
Class of Stock [Line Items]
Revenues		$ 560,244				575,688									$ 2,324,623
Gross profit		62,937				64,458
Asset impairment and mine closure costs						0									0
Income (loss) from operations		50,951				46,118
Reorganization items, net		494				(759)									$ (2,398)
Net income (loss)		$ 81,271				$ 33,449
Diluted earnings (loss) per common share (in dollars per share)		$ 3.64				$ 1.31