OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	$ 1,738,909	$ 755,461
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,738,909	755,461
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	186	47,856
Net Amount	1,475,478	637,283
Repurchase agreements
Gross Amounts of Recognized Liabilities	272,127	418,090
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	272,127	418,090
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	272,127	418,090
Total Liabilities
Gross Amounts of Recognized Liabilities	2,011,036	1,173,551
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	2,011,036	1,173,551
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	186	47,856
Net Amount	1,747,605	1,055,373
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	263,957	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	263,957	125,519
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	186	47,856
Net Amount	526	7,341
Total derivatives, subject to a master netting arrangement or similar arrangement
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	263,957	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	263,957	125,519
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	186	47,856
Net Amount	526	7,341
Embedded derivative - Modco reinsurance treaties
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	245,792	32,828
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	245,792	32,828
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement		0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	245,792	32,828
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	735,465	289,343
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	735,465	289,343
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	735,465	289,343
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	306,063	217,288
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	306,063	217,288
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	306,063	217,288
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	141,793	90,231
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	141,793	90,231
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	141,793	90,231
Other
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	45,839	252
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	45,839	252
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	45,839	252
Total derivatives, not subject to a master netting arrangement or similar arrangement
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	1,474,952	629,942
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,474,952	629,942
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	$ 1,474,952	$ 629,942