Workers' Compensation Expense (Worker's Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accrued Workers' Compensation [Line Items]
Curtailments			$ 3,600
Increase (decrease) in occupational disease liability				$ 10,000
Discount rate used for revaluation				3.86%
Successor | Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	$ 1,558			$ 4,675
Interest cost	1,169			3,506
Net amortization	0			0
Curtailments	(4,660)			(4,660)
Net benefit cost (credit)	(1,933)			3,521
Successor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	3,077			8,487
Successor | Workers compensation
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense	$ 1,144			$ 12,008
Predecessor | Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost		$ 1,051			$ 3,466
Interest cost		1,098			3,184
Net amortization		2,178			4,325
Curtailments		0			4,156
Net benefit cost (credit)		4,327			15,131
Predecessor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments		2,415			6,628
Predecessor | Workers compensation
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense		$ 6,742			$ 21,759