OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	$ 817,705	$ 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	817,705	1,007,572
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	194,876	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	1,727	4,577
Net Amount	621,102	760,890
Repurchase agreements
Gross Amounts of Recognized Liabilities	665,000	885,000
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	665,000	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	665,000	885,000
Total Liabilities
Gross Amounts of Recognized Liabilities	1,482,705	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	1,482,705	1,892,572
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	194,876	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Paid	1,727	4,577
Net Amount	1,286,102	1,645,890
Free-Standing derivatives
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Subject to a master netting arrangement or similar agreement	196,603	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	196,603	246,682
Derivative Liability, Not Offset, Policy Election Deduction	194,876	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	1,727	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	196,603	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	196,603	246,682
Derivative Liability, Not Offset, Policy Election Deduction	194,876	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash/Securities Received as Collateral	1,727	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	126,090	215,247
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	126,090	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	126,090	215,247
Embedded derivative - GLWB
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	199,322	246,755
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	199,322	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	199,322	246,755
Embedded derivative - FIA
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	218,340	218,676
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	218,340	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	218,340	218,676
Embedded derivative - IUL
Offsetting of Liabilities
Gross Amounts of Recognized Liabilities, Not subject to a master netting arrangement or similar arrangement	77,350	80,212
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	77,350	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	77,350	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	621,102	760,890
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	621,102	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	$ 621,102	$ 760,890