Pension Plan and Employee Benefits - Components of Periodic Benefit Costs and Weighted-Average Assumptions (Details) - USD ($) $ in Thousands		3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended		12 Months Ended
	Mar. 30, 2017	Mar. 30, 2017	Apr. 12, 2016	Dec. 31, 2016	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Mar. 29, 2017	Apr. 13, 2016
Weighted-average assumptions used to determine the benefit obligation
Rate of compensation increase						2.98%		2.93%	2.98%
PENSION BENEFITS
Components of periodic benefit costs
Service cost								$ 9,507	$ 9,039
Interest cost								$ 20,860	$ 21,648
Weighted-average assumptions used to determine the benefit obligation
Discount rate						3.73%		4.35%	3.73%
Weighted-average assumptions used to determine the net benefit cost
Expected return on plan assets								5.86%	6.08%
OTHER BENEFITS
Components of periodic benefit costs
Service cost								$ 1,320	$ 1,446
Interest cost								$ 1,465	$ 1,569
Weighted-average assumptions used to determine the benefit obligation
Discount rate						3.47%		4.16%	3.47%
SERP BENEFITS
Components of periodic benefit costs
Service cost								$ 542	$ 494
Interest cost								$ 3,077	$ 3,239
Amortizations
Curtailment charge			$ 3,600
Special/contractual termination benefits	$ 300		$ 3,200
Weighted-average assumptions used to determine the benefit obligation
Discount rate	4.08%	4.08%	4.60%		3.47%	3.70%		4.34%	3.70%	4.22%	4.15%
Rate of compensation increase						5.00%		5.00%	5.00%
SUCCESSOR
Weighted-average assumptions used to determine the net benefit cost
Rate of compensation increase							3.03%	2.93%	2.98%
SUCCESSOR | PENSION BENEFITS
Components of periodic benefit costs
Service cost							$ 6,909	$ 9,507	$ 9,039
Interest cost							15,088	20,860	21,648
Expected return on plan assets							(17,310)	(23,773)	(24,064)
Amortizations
Prior service (credit) cost							(51)	(71)	(71)
Net loss (gain)							8,138	12,312	10,008
Net periodic benefit cost							$ 12,774	$ 18,835	$ 16,560
Weighted-average assumptions used to determine the benefit obligation
Discount rate											4.21%
Weighted-average assumptions used to determine the net benefit cost
Discount rate							4.21%	3.73%	4.27%
Expected return on plan assets							6.21%
SUCCESSOR | OTHER BENEFITS
Components of periodic benefit costs
Service cost							$ 1,112	$ 1,320	$ 1,446
Interest cost							1,237	1,465	1,569
Expected return on plan assets							0	0	0
Amortizations
Prior service (credit) cost							0	0	0
Net loss (gain)							0	135	(50)
Net periodic benefit cost							$ 2,349	$ 2,920	$ 2,965
Weighted-average assumptions used to determine the net benefit cost
Discount rate							4.08%	3.47%	3.81%
SUCCESSOR | SERP BENEFITS
Components of periodic benefit costs
Service cost							$ 571	$ 542	$ 494
Interest cost							2,275	3,077	3,239
Amortizations
Prior service (credit) cost							(50)	(160)	(190)
Net loss (gain)							1,651	2,913	2,105
Net periodic benefit cost							4,447	6,372	5,648
Curtailment charge							0	0	0
Special/contractual termination benefits							0	0	315
Net periodic benefit cost							$ 4,447	$ 6,372	$ 5,963
Weighted-average assumptions used to determine the net benefit cost
Discount rate		4.22%		3.47%	4.15%	4.08%		3.70%
Rate of compensation increase		5.00%		5.00%	5.00%	5.00%		5.00%
PREDECESSOR
Weighted-average assumptions used to determine the net benefit cost
Rate of compensation increase			3.03%
PREDECESSOR | PENSION BENEFITS
Components of periodic benefit costs
Service cost			$ 2,563
Interest cost			6,242
Expected return on plan assets			(6,812)
Amortizations
Prior service (credit) cost			(20)
Net loss (gain)			2,798
Net periodic benefit cost			$ 4,771
Weighted-average assumptions used to determine the benefit obligation
Discount rate			4.62%
Weighted-average assumptions used to determine the net benefit cost
Discount rate			4.62%
Expected return on plan assets			6.21%
PREDECESSOR | OTHER BENEFITS
Components of periodic benefit costs
Service cost			$ 431
Interest cost			476
Expected return on plan assets			0
Amortizations
Prior service (credit) cost			34
Net loss (gain)			181
Net periodic benefit cost			$ 1,122
Weighted-average assumptions used to determine the net benefit cost
Discount rate			4.08%
PREDECESSOR | SERP BENEFITS
Components of periodic benefit costs
Service cost			$ 702
Interest cost			900
Amortizations
Prior service (credit) cost			17
Net loss (gain)			574
Net periodic benefit cost			2,193
Curtailment charge			3,602
Special/contractual termination benefits			3,222
Net periodic benefit cost			$ 9,017
Weighted-average assumptions used to determine the net benefit cost
Discount rate			4.60%
Rate of compensation increase			5.00%