FAIR VALUE OF FINANCIAL INSTRUMENTS - Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Carrying amounts and estimated fair values of the Company's financial instruments
Capital Lease Obligations	$ 1,300	$ 1,700
Assets:
Mortgage loans on real estate	7,724,733	6,817,723
Policy loans	1,695,886	1,615,615
Fixed maturities, held-to-maturity	2,633,474	2,718,904
Liabilities:
Stable value product account balances	5,234,731	4,698,371
Annuity account balances	13,720,081	10,921,190
Other policyholders’ funds	1,128,379	1,267,198
Debt:
Subordinated debt	605,426	495,289
Non-recourse funding obligations	2,632,497	2,747,477
Golden Gate V
Debt:
Non-recourse funding obligations	729,454	681,285
Carrying Amounts
Assets:
Mortgage loans on real estate	7,724,733	6,817,723
Policy loans	1,695,886	1,615,615
Fixed maturities, held-to-maturity	2,633,474	2,718,904
Liabilities:
Stable value product account balances	5,234,731	4,698,371
Annuity account balances	1,671,414	220,498
Other policyholders’ funds	131,150	133,508
Debt:
Bank borrowings	0	0
Senior Notes	1,100,508	943,370
Subordinated debt	495,426	495,289
Non-recourse funding obligations	2,632,497	2,747,477
Carrying Amounts \| Golden Gate V
Debt:
Non-recourse funding obligations	2,600,000	2,700,000
Carrying Amounts \| Level 3
Debt:
Subordinated funding obligations	110,000	0
Fair Values \| Golden Gate V
Debt:
Non-recourse funding obligations	2,500,000	2,800,000
Fair Values \| Level 3
Assets:
Mortgage loans on real estate	7,447,702	6,740,177
Policy loans	1,695,886	1,615,615
Fixed maturities, held-to-maturity	2,547,210	2,776,327
Liabilities:
Stable value product account balances	5,200,723	4,698,868
Annuity account balances	1,671,434	220,498
Other policyholders’ funds	131,782	134,253
Debt:
Bank borrowings	0	0
Subordinated funding obligations	95,476	0
Non-recourse funding obligations	2,550,237	2,804,983
Fair Values \| Level 3 \| Golden Gate V
Debt:
Non-recourse funding obligations		2,800,000
Fair Values \| Level 2
Debt:
Senior Notes	1,065,338	933,926
Subordinated debt	$ 494,265	$ 501,215

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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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Represents the current and noncurrent portions, in the aggregate, of senior notes and medium-term notes.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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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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Including the current and noncurrent portions, carrying value as of the balance sheet date of loans from a bank with maturities initially due after one year or beyond the normal operating cycle if longer.

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The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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Amount due to policyholders for funds held that are returnable under the terms of insurance contracts, classified as other.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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