FAIR VALUE OF FINANCIAL INSTRUMENTS - Valuation of Level 3 Financial Instruments (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) usd_per_policy	Dec. 31, 2017 USD ($) usd_per_policy
Assets and liabilities measured at fair value on a recurring basis
Derivative liability	$ 658,788,000	$ 905,973,000
Level 3
Assets and liabilities measured at fair value on a recurring basis
Financial instruments that are valued using broker quotes	39,700,000	50,000,000
Financial instruments with book value approximating fair value	63,400,000	65,500,000
Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Fair value, assets	421,458,000	504,228,000
Financial instruments that are valued using broker quotes	26,200,000	35,400,000
Corporate securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Fair value, assets	631,068,000	617,770,000
Financial instruments that are valued using broker quotes	13,500,000	14,600,000
Embedded derivative - GLWB | Level 3
Assets and liabilities measured at fair value on a recurring basis
Derivative liability	43,307,000	15,554,000
Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Derivative liability	217,288,000	218,676,000
Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Derivative liability	$ 90,231,000	$ 80,212,000
Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input | usd_per_policy	145	146
Minimum | Discounted cash flow | Corporate securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.0084	0.0081
Minimum | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.87
Maximum | Discounted cash flow | Corporate securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.0300	0.0395
Weighted Average | Discounted cash flow | Corporate securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.0184	0.0106
Liquidation value | Minimum | Liquidation technique | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input, value	$ 85.75	$ 90
Liquidation value | Maximum | Liquidation technique | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input, value	99.99	97
Liquidation value | Weighted Average | Liquidation technique | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input, value	$ 95.36	$ 94.91
Liquidity premium | Minimum | Discounted cash flow | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.0002	0.0006
Liquidity premium | Maximum | Discounted cash flow | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.0125	0.0117
Liquidity premium | Weighted Average | Discounted cash flow | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.0064	0.0075
Paydown rate | Minimum | Discounted cash flow | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.1096	0.1131
Paydown rate | Maximum | Discounted cash flow | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.1311	0.1197
Paydown rate | Weighted Average | Discounted cash flow | Other asset-backed securities | Level 3
Assets and liabilities measured at fair value on a recurring basis
Debt securities, measurement input	0.1203	0.1154
Mortality | Minimum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.87	0.911
Mortality | Minimum | Actuarial cash flow model | Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.37	0.34
Mortality | Maximum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	1.00	1.066
Mortality | Maximum | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	1.00
Mortality | Maximum | Actuarial cash flow model | Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	5.77	1.52
Utilization | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.99	0.99
Policies with one time over utilization rate of specified amount as a percent	10.00%	10.00%
Specified one time over-utilization rate (as a percent)	400.00%	400.00%
Nonperformance risk | Minimum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.0021	0.0011
Nonperformance risk | Minimum | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.2100	0.0011
Nonperformance risk | Minimum | Actuarial cash flow model | Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.0021	0.0011
Nonperformance risk | Maximum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.0116	0.0079
Nonperformance risk | Maximum | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.0116	0.0079
Nonperformance risk | Maximum | Actuarial cash flow model | Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.0116	0.0079
Withdrawal rate prior to age 70 | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.015	0.015
Withdrawal rate | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	1.00	1.00
Lapse | Minimum
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input		0.010
Lapse | Minimum | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.010	0.010
Lapse | Minimum | Actuarial cash flow model | Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.005	0.005
Lapse | Maximum
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input		0.300
Lapse | Maximum | Actuarial cash flow model | Embedded derivative-FIA | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.300	0.300
Lapse | Maximum | Actuarial cash flow model | Embedded derivative-IUL | Level 3
Assets and liabilities measured at fair value on a recurring basis
Embedded derivative liability, measurement input	0.100	0.100