INCOME TAXES - Effective Income Tax Rate and Components of Income Tax and Deferred Liability (Details) - USD ($) $ in Thousands	1 Months Ended	11 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Provisional tax benefit			$ 797,600
Effective income tax rate related to continuing operations
Statutory federal income tax rate applied to pre-tax income		35.00%	35.00%	35.00%
State income taxes		2.00%	0.60%	0.80%
Investment income not subject to tax		(4.30%)	(5.00%)	(2.70%)
Uncertain tax positions		0.20%	(0.20%)	(0.30%)
Federal Tax law changes		0.00%	(183.30%)	0.00%
Other		0.00%	(1.40%)	1.00%
Effective tax rate (as a percent)		32.90%	(154.30%)	33.80%
Current income tax expense:
Federal		$ 5,715	$ 21,853	$ (50,638)
State		(4,244)	4,399	3,919
Total current		1,471	26,252	(46,719)
Deferred income tax expense:
Federal		118,338	(693,860)	240,127
State		11,734	(3,867)	7,560
Total deferred		$ 130,072	(697,727)	247,687
Deferred income tax assets:
Loss and credit carryforwards			209,401	453,880
Deferred compensation			138,945	209,979
Deferred policy acquisition costs			23,876	156,012
Premium on corporate debt			57,402	104,839
Net unrealized loss on investments			0	353,448
Other			28,179	44,956
Valuation allowance			(3,951)	(6,007)
Deferred income tax assets			453,852	1,317,107
Deferred income tax liabilities:
Premium receivables and policy liabilities			573,469	884,255
VOBA and other intangibles			433,321	720,750
Invested assets (other than unrealized gains (losses))			672,549	1,311,866
Net unrealized gains on investments			6,920	0
Deferred income tax liabilities			1,686,259	2,916,871
Net deferred income tax liability			(1,232,407)	(1,599,764)
State based operating loss carryforwards, valuation allowance			5,000	$ 9,200
Change in valuation allowance, before federal income taxes			4,200
Alternative minimum tax credit			8,900
Research and development credits			1,200
State net operating loss carryforwards			22,800
Predecessor
Effective income tax rate related to continuing operations
Statutory federal income tax rate applied to pre-tax income	35.00%
State income taxes	0.80%
Investment income not subject to tax	(3.20%)
Uncertain tax positions	(0.10%)
Federal Tax law changes	0.00%
Other	(0.10%)
Effective tax rate (as a percent)	32.40%
Current income tax expense:
Federal	$ (32,803)
State	1,685
Total current	(31,118)
Deferred income tax expense:
Federal	30,858
State	(67)
Total deferred	$ 30,791
2035
Deferred income tax liabilities:
Net operating loss carryforwards			259,600
2031
Deferred income tax liabilities:
Net operating loss carryforwards			578,300
Foreign Tax Authority
Deferred income tax liabilities:
Foreign tax credits			$ 7,200