Employee Benefit Plans (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2015	Dec. 31, 2014
Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 3,465	$ 4,282	$ 1,734
Interest cost		3,184	3,944	2,914
Predecessor [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	0	9	21,478
Interest cost		9,338	14,604	17,070
Curtailments		454	0	(25,368)
Settlements		0	2,656	646
Expected return on plan assets		(13,623)	(20,367)	(23,756)
Amortization of prior service credits		0	0	(257)
Amortization of other actuarial losses (gains)		3,973	8,850	3,128
Total net benefit		142	5,752	(7,059)
Predecessor [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		393	866	1,649
Interest cost		3,223	1,904	1,841
Curtailments		(970)	0	0
Settlements		0	0	0
Expected return on plan assets		0	0	0
Amortization of prior service credits		(7,854)	(8,335)	(10,003)
Amortization of other actuarial losses (gains)		(849)	(2,109)	(761)
Total net benefit		$ (6,057)	$ (7,674)	$ (7,274)
Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,583
Interest cost	1,126
Successor [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0
Interest cost	2,768
Curtailments	0
Settlements	(135)
Expected return on plan assets	(4,770)
Amortization of prior service credits	0
Amortization of other actuarial losses (gains)	0
Total net benefit	(2,137)
Successor [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	180
Interest cost	978
Curtailments	0
Settlements	0
Expected return on plan assets	0
Amortization of prior service credits	0
Amortization of other actuarial losses (gains)	0
Total net benefit	$ 1,158