Employee Benefit Plans - Schedule of Changes in Projected Benefit Obligations (Details) - USD ($) $ in Thousands	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2017	Aug. 31, 2017	Dec. 31, 2018
Change in projected benefit obligation:
Contribution change per collective bargaining agreement	$ 0	$ 0	$ 350
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost	10,745		1,754
Other Postretirement Benefit Plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of period			1,438
Service cost			35
Interest cost			41
Benefit payments			(426)
Actuarial loss (gain)			556
Contribution change per collective bargaining agreement	0	0	(17)
Projected benefit obligation at end of period	1,438		1,627
Change in plan assets:
Funded status – net asset (liability)			(1,627)
Amounts recognized in the consolidated balance sheets consist of:
Accrued liabilities			(85)
Postretirement benefit obligations			(1,542)
Net amount recognized			(1,627)
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain			558
Unrecognized prior service cost	0		(17)
Total			541
Pension Plans, Defined Benefit
Change in projected benefit obligation:
Projected benefit obligation at beginning of period			157,427
Service cost			434
Interest cost			4,858
Benefit payments			(10,959)
Actuarial loss (gain)			(3,631)
Projected benefit obligation at end of period	157,427		148,479
Change in plan assets:
Fair value of plan assets at beginning of period			162,758
Actual return on assets			(7,105)
Employer contributions			371
Fair value of plan assets at end of period	162,758		145,065
Funded status – net asset (liability)			(3,414)
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost			1,754
Accrued liabilities			(389)
Pension benefit obligations			(4,779)
Net amount recognized			(3,414)
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain			11,322
Unrecognized prior service cost			350
Total			11,672
Accumulated benefit obligation			148,479
Pension benefit payments paid out under lump-sum payout options			10,959
Predecessor | Other Postretirement Benefit Plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	1,490	1,564	1,438
Service cost	12	22
Interest cost	12	33
Benefit payments	(78)	(156)
Actuarial loss (gain)	2	27
Projected benefit obligation at end of period	1,438	1,490
Change in plan assets:
Funded status – net asset (liability)	(1,438)	(1,490)
Amounts recognized in the consolidated balance sheets consist of:
Accrued liabilities	(97)	(143)
Postretirement benefit obligations	(1,341)	(1,347)
Net amount recognized	(1,438)	(1,490)
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain	(1)	0
Total	(1)	0
Predecessor | Pension Plans, Defined Benefit
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	159,028	154,680	157,427
Service cost	140	260
Interest cost	1,574	3,194
Benefit payments	(3,889)	(7,282)
Actuarial loss (gain)	574	8,176
Projected benefit obligation at end of period	157,427	159,028
Change in plan assets:
Fair value of plan assets at beginning of period	162,929	157,714	$ 162,758
Actual return on assets	3,376	11,897
Employer contributions	342	600
Fair value of plan assets at end of period	162,758	162,929
Funded status – net asset (liability)	5,331	3,901
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost	10,745	9,350
Accrued liabilities	(378)	(370)
Pension benefit obligations	(5,036)	(5,079)
Net amount recognized	5,331	3,901
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain	34	0
Unrecognized prior service cost	0	0
Total	34	0
Accumulated benefit obligation	157,427	158,373
Pension benefit payments paid out under lump-sum payout options	$ 3,889	$ 7,282