OFFSETTING OF ASSETS AND LIABILITIES - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	$ 1,547,178	$ 658,788
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	1,547,178	658,788
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	452,562	70,322
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	4,791	47,856
Net Amount	1,089,825	540,610
Repurchase agreements
Gross Amounts of Recognized Liabilities	270,000	418,090
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	270,000	418,090
Gross Amounts Not Offset in Statement of Financial Position, Financial Instruments	0	0
Gross Amounts Not Offset in Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	270,000	418,090
Total Liabilities
Gross Amounts of Recognized Liabilities	1,817,178	1,076,878
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,817,178	1,076,878
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	452,562	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	4,791	47,856
Net Amount	1,359,825	958,700
Free-Standing derivatives
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	458,623	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	458,623	125,519
Derivative Liability, Not Offset, Policy Election Deduction	452,562	70,322
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	4,791	47,856
Net Amount	1,270	7,341
Total derivatives, subject to a master netting arrangement or similar arrangement
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	458,623	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	458,623	125,519
Derivative Liability, Not Offset, Policy Election Deduction	452,562	70,322
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	4,791	47,856
Net Amount	1,270	7,341
Embedded derivative - Modco reinsurance treaties
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	231,516	32,828
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	231,516	32,828
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	231,516	32,828
Funds withheld derivative
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	70,583	95,142
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	70,583	95,142
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	70,583	95,142
Embedded derivative - GLWB
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	248,577	97,528
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	248,577	97,528
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	248,577	97,528
Embedded derivative - FIA
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	332,869	217,288
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	332,869	217,288
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	332,869	217,288
Embedded derivative - IUL
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	151,765	90,231
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	151,765	90,231
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	151,765	90,231
Other
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	53,245	252
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	53,245	252
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	53,245	252
Total derivatives, not subject to a master netting arrangement or similar arrangement
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	1,088,555	533,269
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	1,088,555	533,269
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in Statement of Financial Position, Collateral Posted	0	0
Net Amount	$ 1,088,555	$ 533,269