ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended							11 Months Ended	12 Months Ended
	Jan. 31, 2015	Mar. 31, 2015	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2014
Reclassifications out of accumulated other comprehensive income (loss)
Income before income tax	$ 1,182									$ 399,842	$ 593,997	$ 583,289
Successor
Reclassifications out of accumulated other comprehensive income (loss)
Benefits and settlement expenses, net of reinsurance ceded										(2,539,943)	(2,880,435)
Realized investment gains (losses): All other investments										(166,886)	90,659
Net impairment losses recognized in earnings			$ (10,856)	$ (3,308)	$ (967)	$ (2,617)				(26,993)	(17,748)
Income before income tax		$ 92,827	120,415	133,079	168,661	171,842	$ 122,845	$ 87,260	$ 96,910	399,842	593,997
Tax (expense) or benefit		(29,966)	(48,148)	(39,785)	(56,541)	(56,494)	(41,654)	(26,853)	(33,070)	(131,543)	(200,968)
Net income		$ 62,861	$ 72,267	$ 93,294	$ 112,120	$ 115,348	$ 81,191	$ 60,407	$ 63,840	268,299	393,029
Successor | Accumulated Gain and Loss Derivatives | 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)	(60)
Income before income tax										(131)	(60)
Tax (expense) or benefit										45	21
Net income										(86)	(39)
Successor | 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										281	32,302
Net impairment losses recognized in earnings										(26,992)	(17,748)
Income before income tax										(26,711)	14,554
Tax (expense) or benefit										9,349	(5,094)
Net income										$ (17,362)	9,460
Successor | Pension benefits liability adjustment | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications out of accumulated other comprehensive income (loss)
Amortization of net actuarial gain/(loss)											(1,231)
Amortization of prior service credit/(cost)											0
Amortization of transition asset/(obligation)											0
Income before income tax											(1,231)
Tax (expense) or benefit											431
Net income											$ (800)
Predecessor
Reclassifications out of accumulated other comprehensive income (loss)
Benefits and settlement expenses, net of reinsurance ceded	(267,287)											(2,791,610)
Realized investment gains (losses): All other investments	81,153											205,402
Net impairment losses recognized in earnings	(481)											(7,275)
Income before income tax	1,182											583,289
Tax (expense) or benefit	327											(198,414)
Net income	1,509											384,875
Predecessor | Accumulated Gain and Loss Derivatives | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications out of accumulated other comprehensive income (loss)
Benefits and settlement expenses, net of reinsurance ceded	(36)											(1,777)
Income before income tax	(36)											(1,777)
Tax (expense) or benefit	13											622
Net income	(23)											(1,155)
Predecessor | 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	6,891											76,952
Net impairment losses recognized in earnings	(481)											(7,275)
Income before income tax	6,410											69,677
Tax (expense) or benefit	(2,244)											(24,387)
Net income	4,166											45,290
Predecessor | Pension benefits liability adjustment | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassifications out of accumulated other comprehensive income (loss)
Amortization of net actuarial gain/(loss)	(808)											(8,264)
Amortization of prior service credit/(cost)	31											386
Amortization of transition asset/(obligation)	5											53
Income before income tax	(772)											(7,825)
Tax (expense) or benefit	270											2,739
Net income	$ (502)											$ (5,086)