OFFSETTING OF ASSETS AND LIABILITIES - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	$ 755,461	$ 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	755,461	1,007,572
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	70,322	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	47,856	4,577
Net Amount	637,283	760,890
Repurchase agreements
Gross Amounts of Recognized Liabilities	418,090	885,000
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	418,090	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 Posted	0	0
Net Amount	418,090	885,000
Total Liabilities
Gross Amounts of Recognized Liabilities	1,173,551	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	1,173,551	1,892,572
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments	70,322	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Posted	47,856	4,577
Net Amount	1,055,373	1,645,890
Free-Standing derivatives
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	125,519	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	125,519	246,682
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	70,322	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	47,856	4,577
Net Amount	7,341	0
Total derivatives, subject to a master netting arrangement or similar arrangement
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, subject to a master netting arrangement	125,519	246,682
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	125,519	246,682
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, subject to a master netting arrangement	70,322	242,105
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	47,856	4,577
Net Amount	7,341	0
Embedded derivative - Modco reinsurance treaties
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	32,828	215,247
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	32,828	215,247
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	32,828	215,247
Embedded derivative - GLWB
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	289,343	246,755
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	289,343	246,755
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	289,343	246,755
Embedded derivative—FIA
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	217,288	218,676
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	217,288	218,676
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	217,288	218,676
Embedded derivative—IUL
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	90,231	80,212
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	90,231	80,212
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	90,231	80,212
Other
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	252
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	252
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0
Net Amount	252
Total derivatives, not subject to a master netting arrangement or similar arrangement
Offsetting of Derivative Liabilities:
Gross Amounts of Recognized Liabilities, not subject to a master netting arrangement	629,942	760,890
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	629,942	760,890
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, not subject to a master netting arrangement	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Collateral Posted	0	0
Net Amount	$ 629,942	$ 760,890