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, 2016
Other Postretirement Benefit Plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	$ 1,490
Service cost	12
Interest cost	12
Benefit payments	(78)
Actuarial loss (gain)	2
Projected benefit obligation at end of period	1,438	$ 1,490
Change in plan assets:
Funded status – net asset (liability)	(1,438)
Amounts recognized in the consolidated balance sheets consist of:
Accrued liabilities	(97)
Postretirement benefit obligations	(1,341)
Net amount recognized	(1,438)
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain (loss)	(1)
Total	(1)
Pension Plans, Defined Benefit
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	159,028
Service cost	140
Interest cost	1,574
Benefit payments	(3,889)
Actuarial loss (gain)	574
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
Actual return on assets	3,376
Employer contributions	342
Fair value of plan assets at end of period	162,758	162,929
Funded status – net asset (liability)	5,331
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost	10,745
Accrued liabilities	(378)
Pension benefit obligations	(5,036)
Net amount recognized	5,331
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain (loss)	34
Unrecognized prior service cost	0
Total	34
Accumulated benefit obligation	157,427
Predecessor | Other Postretirement Benefit Plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of period		1,564	$ 2,427
Service cost		22	71
Interest cost		33	65
Benefit payments		(156)	(240)
Actuarial loss (gain)		27	(759)
Projected benefit obligation at end of period	1,490		1,564
Change in plan assets:
Funded status – net asset (liability)	(1,490)		(1,564)
Amounts recognized in the consolidated balance sheets consist of:
Accrued liabilities	(143)		(234)
Postretirement benefit obligations	(1,347)		(1,330)
Net amount recognized	(1,490)		(1,564)
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain (loss)	0		2,574
Total	0		2,574
Predecessor | Pension Plans, Defined Benefit
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	159,028	154,680	162,941
Service cost		260	377
Interest cost		3,194	5,182
Benefit payments		(7,282)	(9,459)
Actuarial loss (gain)		8,176	(4,361)
Projected benefit obligation at end of period		159,028	154,680
Change in plan assets:
Fair value of plan assets at beginning of period	$ 162,929	157,714	154,506
Actual return on assets		11,897	12,253
Employer contributions		600	414
Fair value of plan assets at end of period		162,929	157,714
Funded status – net asset (liability)		3,901	3,034
Amounts recognized in the consolidated balance sheets consist of:
Prepaid pension cost		9,350	8,501
Accrued liabilities		(370)	(367)
Pension benefit obligations		(5,079)	(5,100)
Net amount recognized		3,901	3,034
Pre-tax components of accumulated other comprehensive loss:
Unrecognized actuarial gain (loss)		0	(25,665)
Unrecognized prior service cost		0	(517)
Total		0	(26,182)
Accumulated benefit obligation		$ 158,373	$ 154,044