OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	$ 1,319,193	$ 755,461
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,319,193	755,461
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	210,744	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	11,215	47,856
Net Amount	1,097,234	637,283
Repurchase agreements
Gross Amounts of Recognized Liabilities	60,000	418,090
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	60,000	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	60,000	418,090
Total Liabilities
Gross Amounts of Recognized Liabilities	1,379,193	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	1,379,193	1,173,551
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	210,744	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	11,215	47,856
Net Amount	1,157,234	1,055,373
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	222,116	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	222,116	125,519
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	210,744	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	11,215	47,856
Net Amount	157	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	222,116	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	222,116	125,519
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	210,744	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	11,215	47,856
Net Amount	157	7,341
Embedded derivative - Modco reinsurance treaties
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	188,853	32,828
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	188,853	32,828
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	188,853	32,828
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	471,199	289,343
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	471,199	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	471,199	289,343
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	298,721	217,288
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	298,721	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	298,721	217,288
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	136,660	90,231
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	136,660	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	136,660	90,231
Other
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	1,644	252
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,644	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	1,644	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	1,097,077	629,942
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,097,077	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	$ 1,097,077	$ 629,942