FAIR VALUE OF FINANCIAL INSTRUMENTS - Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Commercial mortgage loans on real estate, net	$ 9,545,793	$ 9,379,401
Policy loans	1,657,530	1,675,121
Fixed maturities, held-to-maturity	2,728,529	2,823,881
Other long-term investments	2,695,664	2,479,520
Liabilities:
Stable value product account balances	5,984,036	5,443,752
Future policy benefits and claims	14,694,473	14,289,907
Other policyholders’ funds	1,691,472	1,576,856
Debt
Non-recourse funding obligations	2,989,340	3,082,753
Capital lease obligations	800	1,000
Carrying Amounts
Assets:
Other long-term investments	1,300,000	1,300,000
Level 3 \| Carrying Amounts
Assets:
Commercial mortgage loans on real estate, net	9,545,793	9,379,401
Policy loans	1,657,530	1,675,121
Other long-term investments	1,218,279	1,216,996
Liabilities:
Stable value product account balances	5,984,036	5,443,752
Future policy benefits and claims	1,634,654	1,701,324
Other policyholders’ funds	101,558	127,084
Debt
Non-recourse funding obligations	2,989,340	3,082,753
Subordinated funding obligations	110,000	110,000
Level 3 \| Carrying Amounts \| Golden Gate and Golden Gate V
Debt
Non-recourse funding obligations	2,700,000	2,800,000
Level 3 \| Carrying Amounts \| Fixed maturities
Assets:
Fixed maturities, held-to-maturity	2,728,529	2,823,881
Level 3 \| Fair Values
Assets:
Commercial mortgage loans on real estate, net	10,055,284	9,584,487
Policy loans	1,657,530	1,675,121
Other long-term investments	1,278,991	1,246,889
Liabilities:
Stable value product account balances	6,163,437	5,551,195
Future policy benefits and claims	1,646,695	1,705,235
Other policyholders’ funds	105,221	130,259
Debt
Non-recourse funding obligations	3,164,771	3,298,580
Subordinated funding obligations	113,729	113,286
Level 3 \| Fair Values \| Golden Gate and Golden Gate V
Debt
Non-recourse funding obligations	2,900,000	3,000,000
Level 3 \| Fair Values \| Fixed maturities
Assets:
Fixed maturities, held-to-maturity	$ 2,947,350	$ 3,025,790

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Non-recourse funding obligations issued by special purpose entities owned by the reporting entity. The funding obligations are direct financial obligations of the special purpose entity and are not guaranteed by the reporting entity.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount before allowance of loans made to policy and contract holders using their life insurance contracts' cash value or separate accounts as collateral. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums over and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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