OFFSETTING OF ASSETS AND LIABILITIES - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	$ 2,681,451	$ 1,547,178
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	2,681,451	1,547,178
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	864,650	452,562
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	4,193	4,791
Net Amount	1,812,608	1,089,825
Repurchase agreements
Gross Amounts of Recognized Liabilities	436,970	270,000
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in Balance Sheet	436,970	270,000
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted	0	0
Net Amount	436,970	270,000
Total Liabilities
Gross Amounts of Recognized Liabilities	3,118,421	1,817,178
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in Balance Sheet	3,118,421	1,817,178
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	864,650	452,562
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted	4,193	4,791
Net Amount	2,249,578	1,359,825
Free-Standing derivatives
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	871,293	458,623
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	871,293	458,623
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, subject to master netting arrangement	864,650	452,562
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	4,193	4,791
Net Amount	2,450	1,270
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	871,293	458,623
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	871,293	458,623
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, subject to master netting arrangement	864,650	452,562
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	4,193	4,791
Net Amount	2,450	1,270
Embedded derivative - Modco reinsurance treaties
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	388,521	231,516
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	388,521	231,516
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	388,521	231,516
Funds withheld derivative
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	66,331	70,583
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	66,331	70,583
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	66,331	70,583
Embedded derivative - GLWB
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	465,012	248,577
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	465,012	248,577
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	465,012	248,577
Embedded derivative - FIA
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	633,350	332,869
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	633,350	332,869
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	633,350	332,869
Embedded derivative - IUL
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	201,331	151,765
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	201,331	151,765
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	201,331	151,765
Embedded derivative - FIA
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	55,613	53,245
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	55,613	53,245
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	55,613	53,245
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	1,810,158	1,088,555
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position, Including not subject to master netting arrangement	1,810,158	1,088,555
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments, not subject to master netting arrangement	0	0
Gross Amounts Not Offset in the Balance Sheet, Collateral Posted, including not subject to master netting arrangement	0	0
Net Amount	$ 1,810,158	$ 1,088,555