OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	$ 835,447	$ 1,007,572
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	835,447	1,007,572
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	270,878	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	10,089	4,577
Net Amount	554,480	760,890
Repurchase agreements
Gross Amounts of Recognized Liabilities	417,094	885,000
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	417,094	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	417,094	885,000
Total Liabilities
Gross Amounts of Recognized Liabilities	1,252,541	1,892,572
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,252,541	1,892,572
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	270,878	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	10,089	4,577
Net Amount	971,574	1,645,890
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Subject to a master netting arrangement or similar agreement	280,967	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	280,967	246,682
Derivative Liability, Not Offset, Policy Election Deduction	270,878	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	10,089	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 a master netting arrangement or similar agreement	280,967	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	280,967	246,682
Derivative Liability, Not Offset, Policy Election Deduction	270,878	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	10,089	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	60,683	215,247
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	60,683	215,247
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	60,683	215,247
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	141,102	246,755
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	141,102	246,755
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	141,102	246,755
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	256,912	218,676
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	256,912	218,676
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	256,912	218,676
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	95,739	80,212
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	95,739	80,212
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	95,739	80,212
Other
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	44
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	44
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0
Net Amount	44
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	554,480	760,890
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	554,480	760,890
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	0	0
Net Amount	$ 554,480	$ 760,890