Workers' Compensation Expense (Worker's Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accrued Workers' Compensation [Line Items]
Curtailments				$ 3,600
Successor | Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	$ 1,559		$ 3,117
Interest cost	1,168		2,337
Net amortization	0		0
Curtailments	0		0
Net benefit cost (credit)	2,727		5,454
Successor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	2,532		5,410
Successor | Workers compensation
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense	$ 5,259		$ 10,864
Predecessor | Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost		$ 1,310		2,415
Interest cost		1,029		2,086
Net amortization		1,006		2,147
Curtailments		4,156		4,156
Net benefit cost (credit)		7,501		10,804
Predecessor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments		1,246		4,213
Predecessor | Workers compensation
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense		$ 8,747		$ 15,017