Pension Plan and Employee Benefits, Benefit Obligation, Plan Assets, and Funded Status (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 30, 2017	Apr. 12, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation			$ 473,197	$ 520,612
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year				403,715
Fair value of plan assets at end of year			403,715	444,089
SERP Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation			76,194	84,339
Change in benefit obligation [Roll Forward]
Curtailments		$ 3,600
Special/contractual termination benefits	$ 300	3,200
Successor [Member] | Other Postretirement Benefits Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year			42,707	44,136
Service cost			1,112	1,446
Interest cost			1,237	1,569
Plan Participants' Contributions			758	1,149
Actuarial (gain) loss			2,292	437
Expenses paid			0	0
Benefits paid			(3,970)	(5,534)
Benefit obligation at end of year		42,707	44,136	43,203
Change in plan assets [Roll Forward]
Expenses paid			0	0
Benefits paid			(3,970)	(5,534)
Unfunded status			(44,136)	(43,203)
Successor [Member] | Pension Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year			499,724	512,785
Service cost			6,909	9,039
Interest cost			15,088	21,648
Plan Participants' Contributions			0	0
Actuarial (gain) loss			6,242	46,686
Expenses paid			(2,025)	(3,020)
Benefits paid			(13,153)	(19,923)
Benefit obligation at end of year		499,724	512,785	567,215
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year			398,515	403,715
Actual return on plan assets			20,378	63,317
Expenses paid			(2,025)	(3,020)
Benefits paid			(13,153)	(19,923)
Fair value of plan assets at end of year		398,515	403,715	444,089
Unfunded status			(109,070)	(123,126)
Successor [Member] | SERP Benefits [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year			79,555	78,045
Service cost			571	494
Interest cost			2,275	3,239
Actuarial (gain) loss			1,152	6,442
Benefits paid			(2,999)	(4,376)
Plan Amendment			(2,509)	180
Curtailments			0	0
Special/contractual termination benefits			0	315
Benefit obligation at end of year		79,555	78,045	84,339
Change in plan assets [Roll Forward]
Benefits paid			(2,999)	$ (4,376)
Predecessor [Member] | Other Postretirement Benefits Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year		43,070	42,707
Service cost		431			$ 1,635
Interest cost		476			1,607
Plan Participants' Contributions		300
Actuarial (gain) loss		0
Expenses paid		0
Benefits paid		(1,570)
Benefit obligation at end of year		42,707			43,070
Change in plan assets [Roll Forward]
Expenses paid		0
Benefits paid		(1,570)
Unfunded status		(42,707)
Predecessor [Member] | Pension Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year		480,062	499,724
Service cost		2,563			10,419
Interest cost		6,242			20,795
Plan Participants' Contributions		0
Actuarial (gain) loss		16,857
Expenses paid		(801)
Benefits paid		(5,199)
Benefit obligation at end of year		499,724			480,062
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		383,532	398,515
Actual return on plan assets		20,983
Expenses paid		(801)
Benefits paid		(5,199)
Fair value of plan assets at end of year		398,515			383,532
Unfunded status		(101,209)
Predecessor [Member] | SERP Benefits [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year		72,315	$ 79,555
Service cost		702			2,705
Interest cost		900			3,056
Actuarial (gain) loss		0
Benefits paid		(1,186)
Plan Amendment		0
Curtailments		3,602			0
Special/contractual termination benefits		3,222			0
Benefit obligation at end of year		79,555			$ 72,315
Change in plan assets [Roll Forward]
Benefits paid		$ (1,186)