Sch I. Schedule of Investments (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	$ 7,823,121	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	8,174,660
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	6,661,711	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	7,008,790
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	7,008,790
All Other Corporate Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	3,529,997	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	3,708,655
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	3,708,655
Asset-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1,714,126	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	1,768,904
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,768,904
United States Government and agencies
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	30,575	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	32,072
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	32,072
State, municipal and other governments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1,387,013	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	1,499,159
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,499,159
Equity Securities, Investment Summary [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	130,479	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	132,968
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	132,968
Banks, Trust and Insurance, Equities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	27,495	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	27,495
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	27,495
Industrial, Miscellaneous, and All Others [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	2,942	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	3,056
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	3,056
Non-redeemable preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	100,042	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	102,417
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	102,417
Mortgages Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	817,184	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	816,471
Real Estate Investment [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	2,115	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,955	[2]
Policy Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	188,254	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	188,254
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	16,348	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	16,348
Other Long-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	7,030	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	$ 9,874

[1] On the basis of cost adjusted for repayments and amortization of premiums and accrual of discounts for fixed maturities and short-term investments; original cost for equity securities, real estate and other investments; and unpaid principal balance for mortgage loans and policy loans.

[2] Amount shown on balance sheet differs from cost due to depreciation and allowance for possible losses deducted from cost.