ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications Out of AOCI (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								11 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Benefits and settlement expenses, net of reinsurance ceded										$ (2,535,388)	$ (2,955,005)	$ (2,876,726)
Realized investment gains (losses): All other investments										(166,935)	121,087	90,630
Net impairment losses recognized in earnings		$ (853)	$ (273)	$ (2,785)	$ (5,201)	$ (10,856)	$ (3,308)	$ (967)	$ (2,617)	(26,993)	(9,112)	(17,748)
Income before income tax		78,096	165,982	133,286	86,644	(67,145)	94,267	260,580	234,979	254,188	464,008	522,681
Tax (expense) or benefit		839,384	(49,016)	(43,654)	(28,305)	15,041	(20,965)	(87,787)	(76,362)	(74,491)	718,409	(170,073)
Net of tax		$ 917,480	$ 116,966	$ 89,632	$ 58,339	$ (52,104)	$ 73,302	$ 172,793	$ 158,617	179,697	1,182,417	352,608
Predecessor
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Benefits and settlement expenses, net of reinsurance ceded	$ (266,575)
Realized investment gains (losses): All other investments	81,153
Net impairment losses recognized in earnings	(481)
Income before income tax	132,847
Tax (expense) or benefit	(44,325)
Net of tax	88,522
Gains and losses on derivative instruments | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Benefits and settlement expenses, net of reinsurance ceded										(131)	(694)	(60)
Income before income tax										(131)	(694)	(60)
Tax (expense) or benefit										45	243	21
Net of tax	(23)									(86)	(451)	(39)
Gains and losses on derivative instruments | Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Predecessor
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Benefits and settlement expenses, net of reinsurance ceded	(36)
Income before income tax	(36)
Tax (expense) or benefit	13
Unrealized gains and losses on available-for-sale securities | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Realized investment gains (losses): All other investments										271	10,453	32,275
Net impairment losses recognized in earnings										(26,992)	(9,112)	(17,748)
Income before income tax										(26,721)	1,341	14,527
Tax (expense) or benefit										9,352	(397)	(5,085)
Net of tax	4,166									$ (17,369)	$ 944	$ 9,442
Unrealized gains and losses on available-for-sale securities | Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Predecessor
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)
Realized investment gains (losses): All other investments	6,891
Net impairment losses recognized in earnings	(481)
Income before income tax	6,410
Tax (expense) or benefit	$ (2,244)