OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	$ 972,965	$ 755,461
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	972,965	755,461
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	165,785	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	9,289	47,856
Net Amount	797,891	637,283
Repurchase agreements
Gross Amounts of Recognized Liabilities	89,275	418,090
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	89,275	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	89,275	418,090
Total Liabilities
Gross Amounts of Recognized Liabilities	1,062,240	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	1,062,240	1,173,551
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	165,785	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	9,289	47,856
Net Amount	887,166	1,055,373
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	175,074	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	175,074	125,519
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	165,785	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	9,289	47,856
Net Amount	0	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	175,074	125,519
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	175,074	125,519
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	165,785	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	9,289	47,856
Net Amount	0	7,341
Embedded derivative - Modco reinsurance treaties
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	107,457	32,828
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	107,457	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	107,457	32,828
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	313,190	289,343
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	313,190	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	313,190	289,343
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	263,445	217,288
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	263,445	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	263,445	217,288
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	112,814	90,231
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	112,814	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	112,814	90,231
Other
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	985	252
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	985	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	985	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	797,891	629,942
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	797,891	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	$ 797,891	$ 629,942