OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives not subject to a master netting arrangement	$ 536,727	$ 605,075
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	536,727	605,075
Derivative Asset, Not Offset, Policy Election Deduction	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	74,202	108,830
Net Amount	279,583	254,140
Free-Standing derivatives
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives	379,860	468,871
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	379,860	468,871
Derivative Asset, Not Subject to Master Netting Arrangement Deduction	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	74,202	108,830
Net Amount	122,716	117,936
Total derivatives, subject to a master netting arrangement or similar arrangement
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives	379,860	468,871
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	379,860	468,871
Derivative Asset, Not Subject to Master Netting Arrangement Deduction	182,942	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	74,202	108,830
Net Amount	122,716	117,936
Embedded derivative - Modco reinsurance treaties
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives not subject to a master netting arrangement	1,551	1,009
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	1,551	1,009
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	1,551	1,009
Embedded derivative - GLWB
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives not subject to a master netting arrangement	155,123	134,995
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	155,123	134,995
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	155,123	134,995
Other
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives not subject to a master netting arrangement	193	200
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	193	200
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	193	200
Total derivatives, not subject to a master netting arrangement or similar arrangement
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives not subject to a master netting arrangement	156,867	136,204
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	156,867	136,204
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	$ 156,867	$ 136,204