INCOME TAXES - Effective Income Tax Rate and Components of Income Tax and Deferred Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective income tax rate related to continuing operations
Statutory federal income tax rate applied to pre-tax income	21.00%	21.00%	35.00%
State income taxes	0.40%	4.20%	0.30%
Investment income not subject to tax	(1.60%)	(4.50%)	(4.70%)
Prior period adjustments	0.10%	1.60%	(1.10%)
Federal Tax law changes	0.00%	0.00%	(184.80%)
Other	(0.80%)	(0.60%)	0.50%
Effective income tax rate	19.10%	21.70%	(154.80%)
Current income tax expense:
Federal	$ 381,202	$ 113,925	$ 39,042
State	9,112	9,699	(2,477)
Total current	390,314	123,624	36,565
Deferred income tax expense:
Federal	(254,184)	(73,364)	(757,748)
State	(5,666)	3,401	2,774
Total deferred	(259,850)	(69,963)	(754,974)
Deferred income tax assets:
Loss and credit carryforwards	132,295	127,168
Deferred compensation	55,559	58,533
Deferred policy acquisition costs	217,967	113,959
Premium on non-recourse funding obligations	784	905
Net unrealized loss on investments	0	373,292
Valuation allowance	(9,153)	(8,629)
Deferred income tax assets	397,452	665,228
Deferred income tax liabilities:
Premium receivables and policy liabilities	211,458	339,555
VOBA and other intangibles	596,756	478,561
Invested assets (other than unrealized gains (losses))	557,763	720,108
Net unrealized gains on investments	376,288	0
Other	27,157	25,343
Deferred income tax liabilities	1,769,422	1,563,567
Net deferred income tax liability	(1,371,970)	(898,339)
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Balance, beginning of period	7,134	11,353	9,856
Additions for tax positions of the current year	0	0	1,857
Additions for tax positions of prior years	0	0	70
Reductions of tax positions of prior years:
Changes in judgment	0	(4,219)	(430)
Settlements during the period	(5,343)	0	0
Lapses of applicable statute of limitations	0	0	0
Balance, end of period	$ 1,791	$ 7,134	$ 11,353