OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Subject to a master netting arrangement or similar agreement	$ 203,002	$ 176,979
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	702,218	571,842
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	905,220	748,821
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	203,002	176,979
Net Amounts of Liabilities Presented in the Statement of Financial Position	905,220	748,821
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	202,402	171,384
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	600	5,595
Net Amount	0	0
Net Amount	702,218	571,842
Repurchase agreements
Gross Amounts of Recognized Liabilities	413,589	797,721
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	413,589	797,721
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	413,589	797,721
Total Liabilities
Gross Amounts of Recognized Liabilities	1,318,809	1,546,542
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,318,809	1,546,542
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	202,402	171,384
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	600	5,595
Net Amount	1,115,807	1,369,563
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Subject to a master netting arrangement or similar agreement	203,002	176,979
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	203,002	176,979
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	202,402	171,384
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	600	5,595
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	196,882	141,301
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	251,363	237,122
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	191,226	147,368
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	$ 62,747	$ 46,051