EMPLOYEE BENEFIT PLANS - Change in Projected Benefit Obligation, Fair Value of Plan Assets, Funded Status, and Amounts Not Yet Recognized (Details) - USD ($) $ in Thousands	1 Months Ended	11 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Successor | Defined Benefit Pension Plan
EMPLOYEE BENEFIT PLANS
Accumulated benefit obligation, end of year		$ 250,133	$ 247,595	$ 250,133
Change in projected benefit obligation:
Projected benefit obligation at beginning of year		281,099	268,221
Service cost		11,220	12,791
Interest cost		9,072	9,751
Amendments		0	0
Actuarial loss/(gain)		(19,235)	5,988
Benefits paid		(13,935)	(30,903)
Projected benefit obligation at end of year	$ 281,099	268,221	265,848	268,221
Change in plan assets:
Fair value of plan assets at beginning of year		201,820	196,042
Actual return on plan assets		6,751	15,815
Employer contributions		1,406	20,889
Benefits paid		(13,935)	(30,903)
Fair value of plan assets at end of year	201,820	196,042	201,843	196,042
After reflecting FASB guidance:
Funded status		(72,179)	(64,005)	(72,179)
Amounts recognized in the balance sheet:
Other liabilities		(72,179)	(64,005)	(72,179)
Amounts recognized in accumulated other comprehensive income:
Net actuarial loss/(gain)		(12,772)	(7,855)	(12,772)
Prior service cost/(credit)		0	0	0
Total amounts recognized in AOCI		(12,772)	(7,855)	(12,772)
Successor | Unfunded Excess Benefits Plan
EMPLOYEE BENEFIT PLANS
Accumulated benefit obligation, end of year		54,196	45,594	54,196
Change in projected benefit obligation:
Projected benefit obligation at beginning of year		51,243	56,985
Service cost		1,229	1,413
Interest cost		1,499	1,353
Amendments		0	0
Actuarial loss/(gain)		4,484	4,124
Benefits paid		(1,470)	(16,073)
Projected benefit obligation at end of year	51,243	56,985	47,802	56,985
Change in plan assets:
Fair value of plan assets at beginning of year		0	0
Actual return on plan assets		0	0
Employer contributions		1,470	16,073
Benefits paid		(1,470)	(16,073)
Fair value of plan assets at end of year	0	0	0	0
After reflecting FASB guidance:
Funded status		(56,985)	(47,802)	(56,985)
Amounts recognized in the balance sheet:
Other liabilities		(56,985)	(47,802)	(56,985)
Amounts recognized in accumulated other comprehensive income:
Net actuarial loss/(gain)		4,484	6,294	4,484
Prior service cost/(credit)		0	0	0
Total amounts recognized in AOCI		4,484	6,294	4,484
Successor | Other Postretirement Benefits
EMPLOYEE BENEFIT PLANS
Accumulated benefit obligation, end of year		100	100	100
Successor | Retiree medical plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	247		137	247
Service cost			0	1
Interest cost			1	2
Actuarial loss/(gain)			(22)	(113)
Plan participant contributions			87	141
Benefits paid			(142)	(141)
Projected benefit obligation at end of year		137	61	137	$ 247
Change in plan assets:
Benefits paid			(142)	(141)
Successor | Group life insurance plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of year			9,063
Service cost			102
Interest cost			338
Actuarial loss/(gain)			604
Benefits paid			(473)
Projected benefit obligation at end of year		9,063	9,634	9,063
Change in plan assets:
Benefits paid			$ (473)
Predecessor | Defined Benefit Pension Plan
EMPLOYEE BENEFIT PLANS
Accumulated benefit obligation, end of year	262,290
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	267,331	281,099		267,331
Service cost	974				9,411
Interest cost	1,002				10,493
Amendments	0
Actuarial loss/(gain)	12,384
Benefits paid	(592)
Projected benefit obligation at end of year	281,099				267,331
Change in plan assets:
Fair value of plan assets at beginning of year	203,772	201,820		203,772
Actual return on plan assets	(3,525)
Employer contributions	2,165
Benefits paid	(592)
Fair value of plan assets at end of year	201,820				203,772
After reflecting FASB guidance:
Funded status	(79,279)
Amounts recognized in the balance sheet:
Other liabilities	(79,279)
Amounts recognized in accumulated other comprehensive income:
Net actuarial loss/(gain)	96,965
Prior service cost/(credit)	(1,001)
Total amounts recognized in AOCI	95,964
Predecessor | Unfunded Excess Benefits Plan
EMPLOYEE BENEFIT PLANS
Accumulated benefit obligation, end of year	49,251
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	49,575	51,243		49,575
Service cost	95				954
Interest cost	140				1,696
Amendments	0
Actuarial loss/(gain)	1,555
Benefits paid	(122)
Projected benefit obligation at end of year	51,243				49,575
Change in plan assets:
Fair value of plan assets at beginning of year	0	0		0
Actual return on plan assets	0
Employer contributions	122
Benefits paid	(122)
Fair value of plan assets at end of year	0				0
After reflecting FASB guidance:
Funded status	(51,243)
Amounts recognized in the balance sheet:
Other liabilities	(51,243)
Amounts recognized in accumulated other comprehensive income:
Net actuarial loss/(gain)	22,401
Prior service cost/(credit)	23
Total amounts recognized in AOCI	22,424
Predecessor | Group life insurance plan
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	9,288	9,781		$ 9,288
Service cost	12	138
Interest cost	39	336
Actuarial loss/(gain)	511	(894)
Benefits paid	(69)	(298)
Projected benefit obligation at end of year	9,781				$ 9,288
Change in plan assets:
Benefits paid	$ (69)	$ (298)