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, 2018	Dec. 31, 2017
Accrued Workers' Compensation [Line Items]
Service cost	$ 1,583		$ 7,440	$ 6,320
Interest cost	1,126		4,365	4,651
Net amortization	0		0	0
Traumatic and other workers’ compensation claims
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense	5,871		17,200	14,179
Total occupational disease
Accrued Workers' Compensation [Line Items]
Service cost			7,440	6,320
Interest cost			4,365	4,651
Total occupational disease	2,709		11,805	10,971
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 3,162		$ 5,395	$ 3,208
Predecessor
Accrued Workers' Compensation [Line Items]
Service cost		$ 3,465
Interest cost		3,184
Net amortization		4,325
Predecessor | Traumatic and other workers’ compensation claims
Accrued Workers' Compensation [Line Items]
Total workers’ compensation expense		17,602
Predecessor | Total occupational disease
Accrued Workers' Compensation [Line Items]
Total occupational disease		10,974
Predecessor | Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments		$ 6,628