OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	$ 711,044	$ 905,973
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	711,044	905,973
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	3,406	4,577
Net Amount	524,696	659,291
Repurchase agreements
Gross Amounts of Recognized Liabilities	39,322	885,000
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	39,322	885,000
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	39,322	885,000
Total Liabilities
Gross Amounts of Recognized Liabilities	750,366	1,790,973
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	750,366	1,790,973
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	3,406	4,577
Net Amount	564,018	1,544,291
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Subject to master netting arrangement or similar arrangement	186,348	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	186,348	246,682
Derivative Liability, Not Offset, Policy Election Deduction	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	3,406	4,577
Net Amount	0	0
Total derivatives, subject to a master netting arrangement or similar arrangement
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Subject to master netting arrangement or similar arrangement	186,348	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	186,348	246,682
Derivative Liability, Not Offset, Policy Election Deduction	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	3,406	4,577
Net Amount	0	0
Embedded derivative - Modco reinsurance treaties
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	76,145	215,247
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	76,145	215,247
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	76,145	215,247
Funds withheld derivative
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	67,688	61,729
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	67,688	61,729
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	67,688	61,729
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	59,128	83,427
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	59,128	83,427
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	59,128	83,427
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	238,569	218,676
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	238,569	218,676
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	238,569	218,676
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	83,166	80,212
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	83,166	80,212
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	83,166	80,212
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 or similar arrangement	524,696	659,291
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	524,696	659,291
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	0	0
Net Amount	$ 524,696	$ 659,291