Workers' Compensation Expense (Occupational Disease Costs Activity and Assumptions) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Self Insurance Reserve [Roll Forward]
Curtailments		$ 3,600
Successor
Self Insurance Reserve [Roll Forward]
Service cost	$ 1,583			$ 6,320
Interest cost	1,126			4,651
Predecessor
Self Insurance Reserve [Roll Forward]
Service cost			$ 3,465		$ 4,282
Interest cost			3,184		3,944
Fresh start accounting adjustment			20,794
Occupational disease costs
Self Insurance Reserve [Roll Forward]
Beginning of period				111,159
End of period	111,159			122,426
Occupational disease costs | Successor
Self Insurance Reserve [Roll Forward]
Beginning of period	119,710			111,159
Service cost	1,583			6,320
Interest cost	1,126			4,651
Curtailments	0			(5,433)
Actuarial (gain) loss	(9,675)			12,242
Benefit and administrative payments	(1,585)			(6,513)
Fresh start accounting adjustment	0			0
End of period	111,159		119,710	$ 122,426
Discount rate (percent)				3.66%
Occupational disease costs | Predecessor
Self Insurance Reserve [Roll Forward]
Beginning of period	$ 119,710	$ 90,836	90,836
Service cost			3,465
Interest cost			3,184
Curtailments			4,156
Actuarial (gain) loss			0
Benefit and administrative payments			(3,728)
Fresh start accounting adjustment			21,797
End of period			$ 119,710		$ 90,836
Discount rate (percent)	4.31%		3.80%