Schedule I - Summary of Investments Other Than Investments in Related Parties Schedule I - Summary of Investments Other Than Investments in Related Parties (Details) (USD $)	Dec. 31, 2014
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 356,209,000
Fair Value	0
Balance Sheet Amount	356,209,000
Corporate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	3,549,000
Fair Value	6,064,000
Balance Sheet Amount	6,064,000
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	9,418,818,000
Fair Value	9,886,820,000
Balance Sheet Amount	9,552,920,000
Public Utility, Equities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	755,000
Fair Value	1,343,000
Balance Sheet Amount	1,343,000
Banks, Trust and Insurance Companies [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,379,000
Fair Value	2,475,000
Balance Sheet Amount	2,475,000
Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	7,116,000
Fair Value	7,421,000
Balance Sheet Amount	7,421,000
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	12,799,000
Fair Value	17,303,000
Balance Sheet Amount	17,303,000
Derivatives, Index Options [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	114,287,000
Fair Value	0
Balance Sheet Amount	114,287,000
Mortgage Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	149,503,000
Fair Value	0
Balance Sheet Amount	149,503,000
Policy loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	63,645,000
Fair Value	0
Balance Sheet Amount	63,645,000
Other Long-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	28,774,000
Fair Value	0
Balance Sheet Amount	28,774,000
Real estate acquired through foreclosure	0
Held-to-maturity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	6,841,543,000
Fair Value	7,175,443,000
Balance Sheet Amount	6,841,543,000
Held-to-maturity Securities [Member] | US Government and Government Agencies and Authorities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	11,981,000
Fair Value	13,095,000
Balance Sheet Amount	11,981,000
Held-to-maturity Securities [Member] | US States and Political Subdivisions Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	432,186,000
Fair Value	463,267,000
Balance Sheet Amount	432,186,000
Held-to-maturity Securities [Member] | Foreign Government Debt [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	0
Fair Value	0
Balance Sheet Amount	0
Held-to-maturity Securities [Member] | Public Utility [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	978,847,000
Fair Value	1,045,926,000
Balance Sheet Amount	978,847,000
Held-to-maturity Securities [Member] | Corporate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	3,754,222,000
Fair Value	3,919,281,000
Balance Sheet Amount	3,754,222,000
Held-to-maturity Securities [Member] | Mortgage-backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,640,582,000
Fair Value	1,705,144,000
Balance Sheet Amount	1,640,582,000
Held-to-maturity Securities [Member] | Asset-Backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	23,725,000
Fair Value	28,730,000
Balance Sheet Amount	23,725,000
Available-for-sale Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,577,275,000
Fair Value	2,711,377,000
Balance Sheet Amount	2,711,377,000
Available-for-sale Securities [Member] | US Government and Government Agencies and Authorities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	0
Fair Value	0
Balance Sheet Amount	0
Available-for-sale Securities [Member] | US States and Political Subdivisions Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	589,000
Fair Value	553,000
Balance Sheet Amount	553,000
Available-for-sale Securities [Member] | Foreign Government Debt [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	9,939,000
Fair Value	10,325,000
Balance Sheet Amount	10,325,000
Available-for-sale Securities [Member] | Public Utility [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	169,179,000
Fair Value	179,216,000
Balance Sheet Amount	179,216,000
Available-for-sale Securities [Member] | Corporate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,334,700,000
Fair Value	2,454,019,000
Balance Sheet Amount	2,454,019,000
Available-for-sale Securities [Member] | Mortgage-backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	48,674,000
Fair Value	52,790,000
Balance Sheet Amount	52,790,000
Available-for-sale Securities [Member] | Asset-Backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	14,194,000
Fair Value	14,474,000
Balance Sheet Amount	$ 14,474,000