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
Liabilities
Fair value	$ 755,461,000	$ 1,007,572,000
Other asset-backed securities | Level 3
Assets
Fair value	421,458,000	504,228,000
Corporate securities | Level 3
Assets
Fair value	631,068,000	617,770,000
Embedded derivative - GLWB | Level 3
Assets
Fair value		111,760,000
Liabilities
Fair value	184,071,000
Embedded derivative—FIA | Level 3
Liabilities
Fair value	217,288,000	218,676,000
Embedded derivative—IUL | Level 3
Liabilities
Fair value	$ 90,231,000	$ 80,212,000
Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	1	146
Minimum | Discounted Cash Flow | Corporate securities | Level 3
Liabilities
Debt securities, measurement input	0.0084	0.0081
Maximum | Discounted Cash Flow | Corporate securities | Level 3
Liabilities
Debt securities, measurement input	0.0300	0.0395
Weighted Average | Discounted Cash Flow | Corporate securities | Level 3
Liabilities
Debt securities, measurement input	0.0184	0.0106
Liquidation value | Minimum | Liquidation technique | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input, value	$ 85.75	$ 90
Liquidation value | Maximum | Liquidation technique | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input, value	99.99	97
Liquidation value | Weighted Average | Liquidation technique | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input, value	$ 95.36	$ 94.91
Liquidity premium | Minimum | Discounted Cash Flow | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input	0.0002	0.0006
Liquidity premium | Maximum | Discounted Cash Flow | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input	0.0125	0.0117
Liquidity premium | Weighted Average | Discounted Cash Flow | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input	0.0064	0.0075
Paydown rate | Minimum | Discounted Cash Flow | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input	0.1096	0.1131
Paydown rate | Maximum | Discounted Cash Flow | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input	0.1311	0.1197
Paydown rate | Weighted Average | Discounted Cash Flow | Other asset-backed securities | Level 3
Liabilities
Debt securities, measurement input	0.1203	0.1154
Mortality | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	1.00
Mortality | Minimum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Liabilities
Embedded derivative liability, measurement input	0.87	0.911
Mortality | Minimum | Actuarial cash flow model | Embedded derivative—IUL | Level 3
Liabilities
Embedded derivative liability, measurement input	0.37	0.34
Mortality | Maximum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Liabilities
Embedded derivative liability, measurement input	1.00	1.066
Mortality | Maximum | Actuarial cash flow model | Embedded derivative—IUL | Level 3
Liabilities
Embedded derivative liability, measurement input	5.77	1.52
Utilization | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Liabilities
Embedded derivative liability, measurement input	0.99	0.99
Policies that have a one-time over-utilization rate of a specified amount (as a percent)	10.00%	10.00%
Specified one-time over-utilization rate (as a percent)	400.00%	400.00%
Withdrawal rate prior to age 70 | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	0.015	0.015
Withdrawal rate | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	1.00	1.00
Lapse | Minimum
Liabilities
Embedded derivative liability, measurement input		0.010
Lapse | Minimum | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	0.010	0.010
Lapse | Minimum | Actuarial cash flow model | Embedded derivative—IUL | Level 3
Liabilities
Embedded derivative liability, measurement input	0.005	0.005
Lapse | Maximum
Liabilities
Embedded derivative liability, measurement input		0.300
Lapse | Maximum | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	0.300	0.300
Lapse | Maximum | Actuarial cash flow model | Embedded derivative—IUL | Level 3
Liabilities
Embedded derivative liability, measurement input	0.100	0.100
Nonperformance risk | Minimum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Liabilities
Embedded derivative liability, measurement input	0.0021	0.0011
Nonperformance risk | Minimum | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	0.0021	0.0011
Nonperformance risk | Minimum | Actuarial cash flow model | Embedded derivative—IUL | Level 3
Liabilities
Embedded derivative liability, measurement input	0.0021	0.0011
Nonperformance risk | Maximum | Actuarial cash flow model | Embedded derivative - GLWB | Level 3
Liabilities
Embedded derivative liability, measurement input	0.0116	0.0079
Nonperformance risk | Maximum | Actuarial cash flow model | Embedded derivative—FIA | Level 3
Liabilities
Embedded derivative liability, measurement input	0.0116	0.0079
Nonperformance risk | Maximum | Actuarial cash flow model | Embedded derivative—IUL | Level 3
Liabilities
Embedded derivative liability, measurement input	0.0116	0.0079