Workers' Compensation Expense (Worker's Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Successor
Accrued Workers' Compensation [Line Items]
Service cost	$ 1,583		$ 6,320
Interest cost	1,126		4,651
Net amortization	0		0
Successor | Traumatic and other workers’ compensation claims
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense	5,871		14,179
Successor | Total occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	1,583		6,320
Interest cost	1,126		4,651
Total occupational disease	2,709		10,971
Successor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 3,162		$ 3,208
Predecessor
Accrued Workers' Compensation [Line Items]
Service cost		$ 3,465		$ 4,282
Interest cost		3,184		3,944
Net amortization		4,325		6,973
Predecessor | Traumatic and other workers’ compensation claims
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense		17,602		31,980
Predecessor | Total occupational disease
Accrued Workers' Compensation [Line Items]
Service cost		3,465
Interest cost		3,184
Total occupational disease		10,974		15,199
Predecessor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments		$ 6,628		$ 16,781